Pretty high bar there. Hell, if you can prove "intent to distribute" beyond a reasonable doubt, then charge the guy with distibution.
If a guy has a distribution amount and is in a place where he can distibute it (on a street corner, in a parking lot, etc.) as opposed to in his living room or basement, then it sure looks like intent to distribute to me. Let's not play games, here.
I'm comfortable with four categories: possession (of a personal use amount), possession (of a distibution amount - no intent to distribute), possession (of a distibution amount - intent to distribute), distribution.