yes Joris, you can easily write your search query to get the wt.representation.Representation first and then you can get the Representable from it(the object for which this Rep is) type cast it, you will get the CadDoc(or any object) and then get the assembly from the EPMDocument. I hope I understood your concern's and replaying back with the appropriate solution,
wt.representation.Representation.getRepresentable()---->Gives you the base object.
