Yeah, but he's not an Avenger in the books. At all.
This is more like making Amanda Waller a founding field-team member of the JLA.
Screw him, with him as a major character in the movie, ACTUAL AVENGERS won't be in the Avengers movie. Sorry Hawkeye, you can't be in the Avengers movie. Someone else is doing the whole "guy with no powers, but he's got good aim" thing, and there's only so much room in the movie!