[EricH]

I'm with Chris that there may be other methods. But, I'm a bit curious about this setup, and here's why:

It sounds like you're trying to power a wheel and a live axle independently from the same gear, which is driven via its gear train. If that's correct, then what's the problem with just driving the axle and using the axle to drive the wheel? A relatively simple key or hex setup will work quite well to do this; you might even be able to do it with a single keyway/key on the axle.