if you establish the precedent that drug use in public is a public nuisance that harms the public rather than try to condemn them for a defect in character or try to order them into treatment against their will, you should be able to get them off the street, but that doesn't give them somewhere to go.

what they want is some backwoods space to get high in.

i say give them a small area around the dump, put a consumption site near it and regularly send firefighters, bylaw and police in to check up. they'll clear out of downtown voluntarily.