On second thought, moving the servo tray forward doesn't look like a practical solution. The three servos would need to be squeezed into the 10-11cm of space between the CG and the wing bulkhead. This might just be possible. But then there would be no way of accessing the fuel tank. Of course, the servo tray could be made removeable but...

...well there's always a way to do anything. The simplest solution though is just to add the weight -- and get out and fly.

BTW, here a photo of the Vanessa Rig I used to check the balance.