You could remove the the motor mount and motor as a whole and then try and position it in a drill press. You will need to clamp the pinion in the vice and then use something else to support the motor. I would only drill down a 10th of inch or so at a time then back it out. Also make sure to cover any openings in the motor so shavings and debris from the drilling don't get in there.
Another option would be to take a dremel with a metal cutting blade to the gear. You'd loose the gear with this, but you might have to make the sacrifice...
Losi 8T 1.0, Savage Flux - XL style, LST XXL, Muggy, 3.3 E-Revo Conversion and sitting outside 425hp, 831 Tq Dodge Ram Turbo Diesel. It SMOKES