The way to go is to try and get a hold of the Specialised RC lipo tray by Corally. Excellent weight balance with the offset design which balances the lipo side in the same way as the motor by hanging it out at the back of the tray.

Also it allows the use of the standard battery brace and posts without the need for spacing or modification and eliminates the possibility of tweak. Further to this it has holes so you can use the Corally screw on balance weights