Ok, here's what you gotta do....
1.)Get a frenched-plate box. (I suggest fbimini.com, they're like $20)
2.)remove old plate spot, fill in the hole.
3.)cut new hole for frenched-plate box, make sure you like the angle, cuz it's there for good. Running lights to the new spot would be a good idea, also.
4.)Set box in, weld it up tight.
5.)Get it painted so your ass-end isn't primer-coated.
Congrats, you now have an angled license plate! I don't like the look myself, but if it's your thing, have fun with it.