I had one of those birds before.... I don't remember the tail falling like that though. Some of my thoughts...

1. CG should be checked withOUT fuel...
2. If the tail falls back without fuel it should work well once fuel is added BUT when you come back after burning off the fuel that tail will simply drop like that again.
3. The purpose of checking for CG is not to control the way it stands on the ground... It's for how it will FLY.

I would maybe move the main mount aft about an inch or so.... Its NOT that scientific. If you move it way back... You will have a little added difficulty in taking off but that would probably if you put it back near the aft servos (elevator/Rudder). one or two inches shouldn't be close enough to the holes you drilled already to compromise the integrity and should still be able to lift off easily. Remember it's a PLANE not a CAR.... balance it to the WING and it will fly great... If you balance it to the wheels then in this case it will be REAL nose heavy and you'll have your hands full!!!

Good luck and let us know how you do! Keep sharing your info....