Damn right I'm a maniac.
I'd say drill two holes in the body/bed mount and run a piece of angle iron parallel to the ground, forward from the bed mount. Attatch with bolts or self-tapping screws. Then get a long piece of threaded rod to use as your flagpole. Drill a hole in the angle iron, and secure the threaded rod with two nuts and a lockwasher. You might want to slip a piece of rubber tubing of some sort over the threaded rod to keep it from scratching up the paint between the cab and bed because there will be a small amount of flex that will probably be unavoidable.