Moving the switch for the ignition near the front and keeping the ignition wires away from the throttle servo and other radio wires should do it. 12" is ideal but not generally possible. Making sure you don't run ignition and radio/servo wires along together side by side is the first objective.

Other things:-
Route your aerial away from any metal pushrods or long servo leads in the tail.
Make sure your battery is man enough for the servos you have. AAs won't fly 5 or more servos in an aerobatic plane.
Add a ground wire from the ignition case to the engine (one of the mounting bolts inside the bulkhead is good). You may have to solder one end to the HT lead braiding if the ignition has a plastic case.