I happened to be thinking of this earlier today and came up with a half theory as long as you are about modding parts to work...

This is the composition of a slipper clutch:

This is the slipper clutch assembly for the Traxxas Grave Digger:

Here is a different one in a nitro truck:

In theory all you need is the appropriate gearing and mod a shaft to work with the mid shaft of the sprint 2 yet hold the slipper clutch assembly together while spacing the motor slightly deeper in the mount(would probably need cut and an adapter plate made). Or mate the slipper clutch to a modded pinion with an e-clip like in the installed pic.