how does the hybrid rule prohibit an electric supercharger? The electric motor doesnt provide thrust for the car and is therefore more like an electric water pump.
If you were going to use some thermoelectric generator and a turbocharger you will want to use the generator after the turbine.
All systems you proposed for generating electric power will be rather heavy and complex. I cant really see the advantage compared to using a battery to store the energy, especially as an endurance is finished in a short period of time. You could also run a bigger alternator on your engine, that is only switched on during overrun. Because of the low power requirement the traction of the rear wheels is not really a problem.