Maybe this is the way to do it...get a spare cover and have this welded to it
...haven't measured exactly, but it should be close. Grind down the ridge so the entire bottom plate touches, coat it in heat sink grease and weld it on...might look a little funny, but probably would be pretty functional!
9000 miles around US 2up on a ratted out 1985 Honda Shadow 500 (VT500c) in under 2 months. If you're interested check our blog
Now riding Central Asia on a black 1994 Dominator.