Not sure if there is a gas tank riser made, but it don't seem to hard to make em.
You can attach (tape) small tubing to the top rail then run the cables through em
If your cables have a cable housing just put a strip of 1/16" rubber over em, or a piece of pipe insulation
Maybe you can fabricate some kind of space with the gas tank mounts.
Easy solution is to run the cables on the bottom