In the admin tool there is a section for file types. By right clicking and selecting 'Properties' on a specific file type, you can specify how that file type reacts in the various tabs, ie. contains, where used, etc. Uncheck the option for 'Do not show "sub-parents" for this file type'. I had to do this for SW assemblies because the users did not want to see the sub-parents for assembly files. One caveat is this is a global setting so it effects all users who view that file type.
Hope this helps.
For those (like me) who are searching past discussions and found this one, please note that the options available in the File Types Properties dialog are now much different (apparently much less flexible) than what Lucas describes for EPDM 2008.