Steve,
Can you remove the fuel tank and then place the battery under where the tank will go, and the replace the tank?? I have done this in several planes were I needed to have the battery up front under the tank. Pull the tank out and slide the battery in place, and then replace the tank.

Personally I prefer to not use heavy hubs for adjusting the CG, because if the engine ever throws the hub and the prop you are left with trying to deadstick a tail heavy plane.

Ken