ORIGINAL: mscic-RCU
You might try putting a strip of 1/8" plywood underneath the rearward mounting flang of the retract to cant the gear forward. I had to do this on my H9 P51. That mod helped tremendously along with using a full max up elevator setting set up as high rate on the transmitter. Unless you can get the wheels even or in front of the leading edge of the wing, taxiing is a problem with taildraggers. As GB said, you are limited as to what you can do with an ARF.
Adding shims under the retracts mount is very common on warbirds and such. I have to shim my P-51's retracts alot and it's still tipsy. It too is a hanger 9......go figure. And what ever you do,dont go adding a buch of tail weight to the plane. Make it balance according to the manuals specs or just very slight nose heavy. Tail heavy planes have VERY sensitive elevators making them very hard to control.....not a good idea for you spit!