Well, you said you already got busted by your own parents. Do your parents and his talk to each other reguarly? Maybe you can play it like this...when dealing with his parents, explain that you were wrong and you didn't mean to get their kid in trouble, yadda yadda yadda, and try to work in that you already got busted by your parents as if to say you already got in trouble for the same thing. Then with your parents, you can probably work it that the weed that was found was leftover from what they had busted you with. Hopefully no one will ask for dates and stuff like that.

That's the punk way out. The mans way out is to face the music with his parents and, as I said before, take the knocks with your own. You made a choice, you have to deal with the consequences. That's the adult way to handle it.