I also like this self balancing vehicle, and I noticed that they were using this motors.
For regeneration brake may be they are using the Smart Pie in the SBU v3, perhaps the best option it is to contact with goldenmotor.com , I don´t think that SBU people will help you because this means loose money for them.
edit: There is a lot of information in goldenmotor forums, I´ve just found this:
I think this would be relatively easy to implement with an arduino, a gyro and doing something really fun!!
PS: please, excuse my english