You've got enough physical space to wind a driver in this way - no barrier there.
The "pickup" coil of your humbucker will have an induced current from the "driver" coil
that may or may not cause resonance/squealing/fizz effects.
The simple solution is to short out (and, if that is not enough, disconnect the ground wire) from the "pickup" coil
during Sustainer operation.
Incidentally,
Your choice of .010 to .052 strings guarantees that you'll get far more sustain out of the lower strings than you can achieve on the top strings (when compared to a lighter-bottom string set).
For the moment, I've learned to live with this, as these string gauges are vital to the feel, tone and tuning stability of my guitar.
