Remember that the CG with an empty tank is the most tail heavy condition, and what that means in terms of the way the plane handles.
Also consider a similar electric powered model CG measured with the battery in place. Despite rumors to the contrary, the battery weight does not change
between fully charged and discharged.
The traditional "cure" for a tank mounted away from the engine was first, a pressurized tank, usually using crankcase or exhaust pressure,
and later, a pump.