fuck the ketchup, just get this:
mix in some garlic/other spices with mutilated moocow before cooking it in the bacon grease. also you should make sure to use the pepper jack no matter what, if you use that mustard.
what kind of bun are you using? this is a key element that is often overlooked. i would brown the buns in the pan after dumping out bacon grease - obv some will still be coating the pan and will make the bun (pretzel roll, preferably) god.
i would also sautee the onions and maybe some white mushrooms in olive oil w/garlic to put on the burger.