Try and move the battery behind the radio compartment. If you need more weight than the stock battery, talk to your LHS and buy an 1100 mAh battery, it will weigh more and help balance the plane, and also give you a lot more cushion on battery charge. I did this as well, and stuck it in place with some double sided foam tape.
Only problem with the Avistar sitting nose high on the ground is if you touch down fast, like I manage to do most of the time, the wing is still flying, and still has angle of attack, so the plane will lift off and bounce. I put a much smaller nose wheel on mine once, and it helped immensely with keeping it on the ground, even when I smoked it in.

Andy