I tried to use the following request and suceed with it:

<wps:Execute service="WPS" version="1.0.0" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 ../wpsExecute_request.xsd">
 <ows:Identifier>getFeaturesCopy</ows:Identifier>
 <wps:DataInputs>
  <wps:Input>
   <ows:Identifier>InputEntity2</ows:Identifier>
   <wps:Reference mimeType="text/xml" xlink:href="http://127.0.0.1/np-bin/mapserv.cgi?map=/Users/djay/Sites/data/Result_79554.map&amp;SERVICE=WFS&amp;VERSION=1.0.0&amp;REQUEST=GetFeature&amp;typeName=Result&amp;__tt=Fri Aug 09 2013 00:52:34 GMT+0200 (CEST)" />
  </wps:Input>
  <wps:Input>
   <ows:Identifier>InputEntity1</ows:Identifier>
   <wps:Reference mimeType="text/xml" xlink:href="http://127.0.0.1/np-bin/mapserv.cgi?map=/Users/djay/Sites/data/public_maps/search_indicateurs_com002.map" method="POST">
    <wps:Header key="Content-Type" value="text/xml" />
    <wps:Body><wfs:GetFeature service="WFS" version="1.0.0" outputFormat="GML2" xmlns:wfs="http://www.opengis.net/wfs" xmlns:ogc="http://www.opengis.net/ogc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wfs http://schemas.opengis.net/wfs/1.0.0/WFS-basic.xsd">
      <wfs:Query typeName="com002">
       <Filter>
        <OR>
         <PropertyIsLike wildcard='*' singleChar='.' escape='!'>
          <PropertyName>num_com</PropertyName>
          <Literal>75105</Literal>
         </PropertyIsLike>
         <PropertyIsLike wildcard='*' singleChar='.' escape='!'>
          <PropertyName>num_com</PropertyName>
          <Literal>75106</Literal>
         </PropertyIsLike>
         <PropertyIsLike wildcard='*' singleChar='.' escape='!'>
          <PropertyName>num_com</PropertyName>
          <Literal>75107</Literal>
         </PropertyIsLike>
         <PropertyIsLike wildcard='*' singleChar='.' escape='!'>
          <PropertyName>num_com</PropertyName>
          <Literal>75108</Literal>
         </PropertyIsLike>
        </OR>
       </Filter>
      </wfs:Query>
     </wfs:GetFeature>
    </wps:Body>
   </wps:Reference>
  </wps:Input>
 </wps:DataInputs>
 <wps:ResponseForm>
  <wps:ResponseDocument>
   <wps:Output mimeType="image/png" asReference="true">
    <ows:Identifier>Result</ows:Identifier></wps:Output>
   </wps:ResponseDocument>
 </wps:ResponseForm>
</wps:Execute>

Nevertheless, when trying to give input references in reverse order it failed by receiving signal 11 (segmentation fault).

So, when using the following request, it failed:

<wps:Execute service="WPS" version="1.0.0" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 ../wpsExecute_request.xsd">
 <ows:Identifier>getFeaturesCopy</ows:Identifier>
 <wps:DataInputs>
  <wps:Input>
   <ows:Identifier>InputEntity1</ows:Identifier>
   <wps:Reference mimeType="text/xml" xlink:href="http://127.0.0.1/np-bin/mapserv.cgi?map=/Users/djay/Sites/data/public_maps/search_indicateurs_com002.map" method="POST">
    <wps:Header key="Content-Type" value="text/xml" />
    <wps:Body><wfs:GetFeature service="WFS" version="1.0.0" outputFormat="GML2" xmlns:wfs="http://www.opengis.net/wfs" xmlns:ogc="http://www.opengis.net/ogc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wfs http://schemas.opengis.net/wfs/1.0.0/WFS-basic.xsd">
      <wfs:Query typeName="com002">
       <Filter>
        <OR>
         <PropertyIsLike wildcard='*' singleChar='.' escape='!'>
          <PropertyName>num_com</PropertyName>
          <Literal>75105</Literal>
         </PropertyIsLike>
         <PropertyIsLike wildcard='*' singleChar='.' escape='!'>
          <PropertyName>num_com</PropertyName>
          <Literal>75106</Literal>
         </PropertyIsLike>
         <PropertyIsLike wildcard='*' singleChar='.' escape='!'>
          <PropertyName>num_com</PropertyName>
          <Literal>75107</Literal>
         </PropertyIsLike>
         <PropertyIsLike wildcard='*' singleChar='.' escape='!'>
          <PropertyName>num_com</PropertyName>
          <Literal>75108</Literal>
         </PropertyIsLike>
        </OR>
       </Filter>
      </wfs:Query>
     </wfs:GetFeature>
    </wps:Body>
   </wps:Reference>
  </wps:Input>
  <wps:Input>
   <ows:Identifier>InputEntity2</ows:Identifier>
   <wps:Reference mimeType="text/xml" xlink:href="http://127.0.0.1/np-bin/mapserv.cgi?map=/Users/djay/Sites/data/Result_79554.map&amp;SERVICE=WFS&amp;VERSION=1.0.0&amp;REQUEST=GetFeature&amp;typeName=Result&amp;__tt=Fri Aug 09 2013 00:52:34 GMT+0200 (CEST)" />
  </wps:Input>
 </wps:DataInputs>
 <wps:ResponseForm>
  <wps:ResponseDocument>
   <wps:Output mimeType="image/png" asReference="true">
    <ows:Identifier>Result</ows:Identifier></wps:Output>
   </wps:ResponseDocument>
 </wps:ResponseForm>
</wps:Execute>

There should be something specific to be done to handle correctly the header setting / clearing for POST requests. Anyway, it should work whatever is the order of input references.