If you have to add weight (battrey relocation doesn't work) then I suggest drilling, or cutting a 1/2" hole as close the rear of the fuse as you can on the bottom side. Hang the plane up by the prop and insert enough "Bullet" shaped lead fishing weights coated with epoxy until you get the CG you're looking for. To accurately do this, you will need to know how many weights is required before you start stuffing the weights in. Also account for a little extra weight that the epoxy will add. Keep the plane suspended by the prop until the epoxy has curred. A small covering patch over the 1/2" hole and you're almost done. Double check the CG. Now you're done!