It's not rusting from underneath, so it's probably not going to rust much farther, not to mention it's not going to get as much road-crap salt on it up on the hood.
But... you can get 'Rust-Mort' or Naval Jelly. Both should do the trick. I've used Rust-Mort before and it worked. It's a liquid (you'll probably have to clean the wax off of that area first) that you just dab on the affected area with a cue-tip or something. Just tape off that area. After a few times (let dry in between) It will turn the rust into a hard black substance that no longer oxidizes (rusts). Then prime and touch up when you can.