Leaving it out it the air will dry it naturally. You dont wont to speed dry it as it will taste nasty as hell. I think you dealer is taking the piss a bit by saying 'put it on a radiator'. He shouldnt be selling damp weed. Out of that 28g you could proberly lose a 7g of weight from the water depending on how wet it is. If a dealer tryed to sell me an oz of damp bud id tell him to keep it. Dont be scared of confronting a dealer is he is selling you shit, its your money.

It isnt ok to keep it damp for that amount of time. It will go mouldy and trust me you dont want to be smoking mold.