if you put the mount for a caliper on the front of the wheel technically the direction of disk movement will pull the caliper downward, so welding won't be neccesarily be needed, as long as you make a good mount that clamps to the fork. as long as it stays on the fork you're fine, since you really only work with forces in one direction.
does that make sense?
actually, you'd probably need to weld to make the clamp, but not weld it to the fork. you might even be able to do that really easy.