Modelling of flexible elements in pro-e.

Does anyone know how to model flexible elements made of rubber like, boots, bellows , gaiters, springs and belts in pro-e. ?

modelling these things in pro-e is no big deal as they can be easily modeled like any other solid metal components.

but the trouble is that once these models are saved as part-files and imported into assembly files for assembly, then it is required that their shapes change (either expand or contract), to fit correctly into the final assembly.

it is just like with the physical components. for example, a belt in the free state , has a different shape, but once it is fixed over pulleys, it takes on a different shape.

does anyone know how this can be done ?