Ward, I'm not sure. My steaming light is an old Perko (I guess, they used to use Perko stuff.) As I recall, there was a plastic spacer which fitted the curve? Can I even remember when I replaced the bulb before I stepped the mast?
If you think about it, there really shouldn't be anything impinging on the fixture. The leech of the jib should be well forward of the steaming light. You'd need a pretty big genoa to hook on a fixture that high. So, if that's the only thing likely to catch on the fixture, could you just screw into the mast, and have the back of the fixture tangent to the curve of the mast? I think so... On the other hand, if you were quite concerned about it, maybe you could make a sweet base plate/spacer out of mahogany or teak...
I think the first step would be to call and talk to Rudy about it, and then call and talk to Hella about it. See what they say. Honestly, I don't have enough experience to advise. Just a certain amount of legal paranoia now that I've changed out my incandescents with LED, thus altering a system. Theoretically, it works the same as the old system with the incandescent, but if there were a legal challenge (like, I got run over by a drunken powerboater...) then their lawyers would have a field day that I am liable for changing out the incandescents for the LED. Just sayin'...
Not a real big concern on my lake, but stupid that I have to think of this kind of thing anyway...
Brian