I found an article in Woodsmith Issue 188 where they make an auxillary fence. They attach a narrow (matching the height of the Kreg fence) piece of MDF or PW, to the Kreg fence with Rockler Universal Fence clamps - see pic. Then simply screw a piece of melamine or whatever, at the height you need, to the mdf/pw unit - cut a clearance hole for the router bit and your done.
I can't complete the jig for a couple days because I doing finishing in the shop now. (ah the joys of a small shop)
May the grain be ever in your favor.