striderjg,
Unless you're 100% sure of what you're doing I wouldn't recommend modifying structural components such as the formers. It's too easy to weaken one to the point that it could break. Do as you've already done and move the battery back as far as you can first. Then you need to add weight to the tail to balance the plane.

I would recommend that you install all of your radio equipment before you balance the plane. The radio components could change the balance of the plane. It's also possible that you could use the receiver itself to help shift the balance of the plane back some. But if you balance the plane and then install the radio equipment there is a good chance that you'll chance the CG of the plane.

Hope this helps

Ken