Some things you can do to increase the roll rate:
1) Increase the control surface deflection--mechanically or electronically. Move the pushrod to the outter most hole at the servo, and the inner most hole at the aileron. This will cause the aileron to travel farther. Be careful, though, that you don't cause anything to bind, or over-extend your servo's ability to handle the stress applied to it. This can also be accomplished with a computer radio using the EPA's, but is better done mechanically.

2) Seal the hinge gaps. This forces air over the surface, and doesn't allow air to pass through the hingeline. Air passing through the hingeline does nothing to help the aircraft change heading.

3) Clip the wing--shorten the wing by one or two bays. Requires some surgery, but if you've already built kits, you should be able to handle this.

4) Install larger ailerons--again, see #3

Good luck..