Tell him that either he goes to the program and successfully completes it or you're not paying for his college.
Also tell him that if he gets below a (you fill in the blank here) average first semester in college, and has any disciplinary problems there, you'll stop paying for college.
Those who hold the gold make the rules.
Don't fool yourself and think that college will magically change him. If he's smoking dope and not following through on his responsibilities when living in your house, he'll do even less when he's no longer under your supervision.While he may want to go to college, sounds like his behavior indicates that he wants to go to college for the wrong reasons: partying, being away from home, etc.
Don't throw your money away when there's no indication that your son yet has the maturity to handle college.
Also expect him to earn money to handle some of his college expenses such as paying for his books and entertainment. If he's not willing to work to do those things to support his dream, why should you give him your hard earned money?