1/16" gap is perfectly acceptable for a control surface on a trainer (Most people use the width of a "T" pin as a guide. Soooo.... my recommendation. just go ahead and mount it with the CA hinges (if they are CA hinges). Put a T-pin through the center of each hinge. Get them all lined up and ready for the CA. Then, working from one side, drop the CA on to the hinge when there is the t-pin width gap. Move on to the next hinge. Do the same there, and keep going. This way, there will be a very slight difference in tension accross the CA hinges on the control surface, but it will essentially be pulled straight by the hinges (CA Hinges will deal with this just fine).

If you feel uncomfortable with the pressure that the elevator will put on the hinges, then just mount it equally uneven (so that the closest part to the stab is at the center of the elevator. If the gaps at the outside of the elevator is much more than 1/8", then have a look into "sealing" hinge gaps.

gus