Hello bcjm,
I am glad you could do a permenant "weld in" repair. This is the most desirable choice.
I realize not everyone can do a professional undetectable "weld in" repair by themselves and must take temporary measures.
A good temporary fix which will slow down or stop the cancer, and allow you to use your car till better repairs can be made;
For the amatuer I would recomend that you mechanically clean the rust with a wire cup prush on a wheel first. Go to an autparts store and get some rust remover/preventer chemical and treat the area. Next go to your local hardware or department store and pick up some rustoleum damproof primer (rusty metal primer), and coat the area. Next coat with a finish rustoleum enamel. After all is dry cover the hole with whatever works, rivet, glue or screw it in place. A little paintable calk to seal, and repaint. A little good ruberized undercoat is optional. The Eastwood Co. also carries a complete line of these types of products.