setting up ailerons

Still working on my H9 Twist and I have a question. I am finishing off connecting the pushrods for the ailerons and... How do you establish a centered/neutral position for the ailerons on a symmetrically airfoiled wing? On a flat bottom or semi-symmetrical you can use the bottom of the wing as a guide. Is there a simple way to hold the ailerons in a neutral position without buying anymore gadgets? One thought I had is to use a small bar clamp with padding, thinking that the pressure on both sides would hold the aileron in place. However I doubt that I could establish the same position on both sides. Any advice is appreciated. TIA