If you are willing to improvise a bit, a solution is out there. I made my own panniers from a design I saw on tour. Basically, to prevent heel strike, I took an L bracket (a small one, like for shelving) which I had bent a little bit in a vice so that one side of the L had more of a "C" shape to it--and attached it to my panniers on the inside where it contacts the rack, just above the chainstay (I drilled a hole, used oversized washers on the inside and outside of the pannier).
Then I put the panniers on and canted them a bit so that the bottom of the pannier pointed to the rear of the bike a few degrees. It was held in this position by the modified L bracket, which contacted and looped around one of the downtubes of the rack.
I hope this makes sense and helps.