In that case, just cut an access panel around the jack point at the outer sill about 15cm either side of the jack point, grind/cut off the old jack point, ensure that the inner sill panel is in good condition, rose weld the new jack point to the inner sill where the old one was, fabricate a repair panel for the hole you cut in the outer sill.
Use Branox on all the exposed metal areas, then prime & paint. leave a small (10mm) hole through which you can inject waxoil when finished and the insert a rubber bung in that hole to prevent water ingress and voila!
Enjoy!