Can I export sub-assemblies defined relative to the origin of the main assembly?

I have a big assembly composed of parts and sub assemblies. I'm trying to create an SDF robot description file from this assembly, and so I'd like to export all the sub-assemblies as STL's and calculate their inertial properties. The problem is that I need the exported STL's to be defined relative to the main assembly origin, but they are exporting relative to their individual sub-assembly origins instead. It will take a lot of work to move things around correctly or calculate the relative poses of all these parts. Is there some way to easily get this to export relative to the main assembly instead?