Saving V5 assembly as V4 session?

OK, so I have a very large V5 multi level assembly with constraints applied. How do I save this entire assembly back to V4? The assembly will not fit into a single V4 model. It seems like I have to save it 1 part at a time? Documentation does not point me towards the solution. Any suggestions or restrictions you are aware of?
Please do not tell me to go via iges or step!

Author: jd_catia