You need the MFLB tubing to have the Underdog stems fit on the Hammer, I have a couple videos that show my using my UD gong, and if the tubing exceeds the heat exchanger the NonG's can be used with two hands.
Cheapest I know is Magic Flight themselves, some other retailers like Planetvape, PIU, etc may also have a foot of the magic flight draw whip, and you might be able to use an FC discount buts going to be around 8 to 15 USD with a foot of tubing and shipping.