Lets be reasonable, welding a plate over it unless done by a highly qualified welder and being heat treated would be worse. At this grade of steel + thickness of the material probably wouldnt be alot more maluble than an alloy frame, so bending it back out, would only make things MUCH worse. Just get in touch with the manufacturer or leave it and zip tie a peice of curved carbon fibre or some hose pipe to the chainstay