Assemblies vs. parts in motion studies

Let's say we have assemblies with some sub-assemblies. Often is hard to select one subassembly, because usually only parts of it are selected.

And in a 3D contact this is pretty messy, a lot of contacts being ignored. Or sometimes a lot of 3D contacts needs to be defined.

Is there a way to make a subassembly to fully integrate its parts and if one piece of it is clicked to select the whole thing and to "behave" in a 3D contact?

To cope with the problem I have saved the needed sub-assemblies as parts, but perhaps there's a better way.

So, what do you do in this situation?

Thank you!

SolidworksMotion Studies