Actually, you may not have to fabricate anything more. My Papamotor setup uses both the thumb throttle and the PAS to activate the hub motor. I use the thumb throttle to get me moving from a standstill and about two seconds later switch to using only the PAS. If you were to use the thumb throttle for the front hub motor and the PAS from the second controller to power the rear hub motor you'd have your solution. In this case, I think the twist throttle would actually be better due to the fact that you could have the front hub motor on for long periods of time and the twist throttle would be more comfortable. Then around corners just stop pedaling and use just the twist/thumb throttle to pull you through.

Now, if you could only get the front hub motor to use a rotor and a hydraulic brake instead of the v-brakes you'd have an amazing e-bike setup. You'd have to modify the e-brake sensor to work with the hydraulic brakes if you wanted the e-brake features. An e-bike like that should be able to haul not just you but an additional 200+ lbs in cargo weight. It would take care of the slow starts from a standstill and allow you to pull through tough headwinds.

If you were to install my future battery carrying system you would be able to go anywhere from 50-100 miles at 30+ mph. An e-bike that can do all that using a hub motor setup would be worth its weight in gold.