Okayyyyyyy.....could you expand a bit perhaps? I mean, would it be ALL convicted drug dealers? Like the kid pimping a roach to his buddies? Or, just the hardcore felons like the guy who blew himself up making methadone for the upteenth time? (Actually, come to think of it, he's probably already gassed). Then, there's the issue of the gas.
What kind of gas would you use? Maybe methane? It's green, organic, renewable - highly renewable. It might not be quick, but it would be pretty unpleasant.
If we make it so hard on the user that the demand drys up then there are no pushers. There is just way too much money involved and addicition causes people to do some really crazy things.