whatever you do it needs to be clean and dry which is difficult to do if your not removeing the sump, it will weep a little oil for ages unless its emptied and cleaned from the inside.

if you can get it clean and dry I think I would jb weld a piece of tin to it, ive jb welded a self tap screw in the bottom of a block that was porous and leaking a jet of water in the sump and its still going strong so far, touch wood lol