Documenting sourced assemblies

I can't believe I am the only person having this problem, so I am hoipeing someone has come up with a soultuion already.  Normally every item weuse gets assigned a part number.  This works fine except for "assemblies" that we buy from other vendors.  For us, this is typically hinges and linear actuators.  So far, I have been creating a hinge part, with each half and the pin as a configuration, and then creating an assembly file.  The problem with this meathod is that when I do a bill of materials, it doubles or triples the hing count.  It seems like what I want I need is a multibody part, but I can't seem to make a multibody part flexible.  Does anyone have any idea on how to make a functional hinge or say a hydralic cyclinder as a single file with all the limit mates of a normally assembly?  I am using solidworks 2011.

Thanks

Chris

SolidworksAssemblies