What radio do you have? We might be able to work out a programmable mix and fix it. You'd have to run the nosewheel on a seperate channel and servo so that it wouldn't move when your gear is up.

Another option is to get the servo saver connections that have a spring in them. They allow the pushrod to move a little without the servo moving. You can connect one to the nosewheel arm, and it would give some in that one direction. You might not have enough power to control the nosewheel though.

The one I saw had pull/pull on the nose gear with cables. When the gear was up the cables had slack and didn't efect the rudder.
later daveo

Make sure your servo connection for the gear is on the closest hole to the servo screw. You don't need much travel for steering