I want to create a bellows boot as a part that I could use in multiple assemblies.  I figured out how to make the profile sketch so it can move correctly.  I got it to work by constraining one end of the bellows to the moving part in my assembly using a sketch relation in the bellows profile.  However, this has 2 drawbacks:

1. I will have to modify the bellows part each time I use it to add the sketch relation to the profile.  This will require making independent versions of the part each time.
2. The bellows doesn't move in real time.  I move the constraining piece, then rebuild the assembly to have the bellows adjust length.  I could live with this more than I could live with #1.

Ideally, I would like to be able to constrain the moving end of the bellows to the mating part in the assembly using an assembly mate.  Then I wouldn't have to make any changes to the bellows part itself.  When I try this, Solidworks treats the bellows as a fixed length part.  The assembly mate does not have the power of the sketch relation.

Is there a way around this, similar to setting an assembly to flexible?  Or is there another method to make a flexible part without having to make the part independent and change it every time you use it?

Thanks,

Marty