You might try a servo reversing Y-harness. I'm using one on my Razzle 3D plane. I think it was either from Cermark or from Expert electronics. This Y-harness that I'm using has an adjustment pot. to center the second servo. You can get nearly equal throws just by doing that. If you use a control horn that is basically a screw with an end fitting, then you can also adjust the distance from the hinge line to increase or decrease throws.
Hope this helps