I have two assemblies that share many components.  I would like to copy parts from one and past them into the other.

Is there a way to copy several parts at one time keeping the mates that are between the copied parts?

I tried to create subassemblies of the parts to be copied, thinking I could then just drag over the subassembly but the "form subassembly here" command is not always available.  Is there another way?