i just stick a screwdriver in the end of the motor so it cant move and screw the wheel on.

as for mounts what i do is drill lots of holes so they make a 3 by 2.5cm rectangle then it remove the center and file it untill a drill motor can fit in, then its only a case of using a hole saw on another bit of plastic for the end of the motor to slot in. total cost of about 5 quid.