use the eyelets on the edge of the rack top. Mount the light under the rack. You could make something or modify the mount. Lots of pictures out there on the web, I'm surprised nobody answered this.

If that's one of the stainless VO racks like I think it is, you can have a mount brazed or welded to it. But people use p-clamps as well as those eyelets.

This thread should be helpful