Use the correct size easy-out... you may have to drill to get to the right size. They do make small ones. Search easy-out screw extractor.
You could also drill the head off then remove the remaining with pliers after the motor is out. go slow and easy, again with the right size bit.
(Xray T3'12 / Tekin RS Pro/ Tekin 10.5), (Xray T3'12 / Edge/ Ballistic 25.5), (F109/ Edge / Ballistic 21.5), (FGX/ GTB2 / Ballistic 21.5), (AE 12r5.1.1 / LRP SXX v2 / Orion 13.5), (AE 10R5.1.1 / Tekin RS Pro / Reedy 8.5), (AE B4/ Tekin RS / Tekin 13.5)
Yeah, they are all RTR!... What class do YOU want to run? VTA, Oh.. :(