buy yourself balanced syringes with something in. I'm sure you and your GM can come up with something that would work.
As for melee weapons, I'm not sure if it was in Shadowrun, but I've seen somewhere a system where in the hilt of the blade there was a vial with extra doses and there were some grooves in the weapon. That way you could recoat by pushing a button, which would fill the grooves with a new dose. Do damage et voila, a new dose of poison. I would say pushing the button is free action.