It is possible with systems with regenerative breaking to charge the battery while pedalling. In our Citroen CZero that would sometimes give 1-2 % charge on a 1.5km downhill brake. But in a car the weight makes all the differance- higher inertia @ kinetic energy. With the bikes 20 kg and your 80kg there simply is not enough weight...to store anything downhill.
The regenerative componentry in Magic pies,Smartpies etc are also heavier. Our hubmotors weigh 2.8 kg - the 'magic' ones from 7,3-9,1 kg. It's much more efficient and cheaper to plug your bike in a charge it, than to use pedal power. 20c of electricity would be about $20 worth of food if you were to pedal!