I've tried alumiweld rods, and couldn't get them to work very well at all. Even with oxy-acetylene heat, freshly ground and prepared surface, etc. I had very, very poor results.
I pulled apart a CX500 motor once to find part of the water jacket around the cylinder replaced with JB Weld. The motor was running and the head gasket wasn't leaking. Granted the steel cylinder and the metal ring of the head gasket does most of the sealing there, but still, I was impressed that it held up, especially with the heat cycles of a cylinder head. So I gave it a try here, and surprisingly it worked. As I remember now, two of the holes were made by putting greased bolts in the remainder of the old threads, and packing the putty around them. There was still a significant amount of the original boss left, and original threads helped hold the bolt in place. The final one at the bottom was drilled, tapped, and helicoiled, as there was no part of the original boss left there, so it was necessary to use a helicoil.
There is only oil splash under that cover, not high pressure oil; that is likely why I didn't have any problems.
If I still had the bike today, I'd likely look into permanent repair options. Or maybe I'd just put a case guard on it and continue riding until it failed. I dunno. It's hard to argue with no leaks and no issues for 10k miles.
Charles.