Which motor is this? If it is a Feigao. If I understand your problem correctly. You can remove the end bell but ultimately you may have to drill an tap new mount holes if you need the the wires in an exact spot. Better yet, with the Feigao you can also pop out both end bells position the shaft side end bell where you want it then epoxy it back together. I would use the RC-Monster motor heatsink/clamp regardless on a Feigao.

You probably have additional mounting holes in the motor already are you sure you can't use the other mount holes? If you have any pics of the problem that might help.