There is a guy, jddcircuit, has been sorting out an all electric prius. Even came up with an integrated charger concept that uses both motors as inductors.
I recall something about welding on the synergy drive, if you do it right, the motors will be in phase and just need one logic controller, and you can still re-purpose the inverter too, i *think*.
Edit, here is the page with the planetary welds, don't think this is jddcircuit though:
http://99mpg.com/ProjectCars/evinsight/