Word of caution on that one. I would strongly recommend you don't add any material to the ailerons themselves, but just let them sweep against the plates that attach to the wing tip. The reason? FLUTTER! Control surfaces as large as those are already prone to flutter, and adding weight and mass to them aft of their local cg will exaserbate the condition, probably with catastrophic results. Just make the tips wider to accomodate the aileron travel, even if they are a funny shape. I feel you will be much better off.

As for the wing rock upright and not inverted. That condition supports what I believe to be the real culprit with this airplane. It's not a function of the wing or wing tips, but rather a function of YAW stability, that is substantially reduced when the vertical tail is blocked by the fuselage and horizontal tail. I have already added a dorsal fin to my Funtana 90 to improve the knife edge flight, but now I think a VENTRAL fin may be the fix for the wing rock. The reason the tip plates helped, in my opinion, is because they added side area and perhaps increased yaw stability. Just a thought