If You do not have the rudder servo in the tail it could solve the nose heavy problem also.
A 40 gram servo in tail will help much here. I have my Futaba S9551 servo for rudder in tail and have no CG problem (in my Wind S 50E) despite I use 6 cell 5000 mAh (Gens ace 45C) that weight about 780-790 gram. Maybe You have the rudder servo in tail and then You have to figure out someting smart, like the cage maybe, to get battery more to the rear.

/Bo