What I'd probably do in this case would be to take two stainless steel "fender washers", maybe about 1 1/2" in diameter.
Bend them to the shape of your B-Stay. Drill the hole out to match the brake bolt on the rear side (rearward facing), and to match the smaller diameter shoulder of the recessed nut on the front side (forward facing). Grind the lower edge to match the wheel well. Then epoxy it all in place, perhaps adding the original tube if the OP still has it.
Using a bolt or dowel or twig, brake bolt, or something to help center it all.