I'd try taping some various stuff to the tail to see what it needs to balance. Even if you don't have lead, you might get away with a few self tapping screws or a bigger tail wheel, etc. You could even toss in a second battery pack aft of the CG if you have one. Whenever I am forced to add weight, I at least like to make it functional weight if at all possible.

Another option might be to push the engine closer to the firewall if that's possible.

Maybe ditch the spinner if you are using one?

A nose heavy plane is definitely more desirable than an extremely tail heavy one but they still aren't much fun.