I think you should be able to get your massage, provided you have enough time in your transfer. When you arrive, there are smoking rooms on Level 2 to have your cigarette if you want. After that, with your domestic boarding pass in hand, head up to the next level, through the security checkpoint. Go to the spa lounge and get your massage. Then go back to Level 2, and go through the international-to-domestic transfer point and on to your domestic gate, the TG domestic lounge, or whatever else you might want if time allows.

From the posts I've seen, nobody has yet tried this, so not sure if a domestic C boarding pass will get you into the spa lounge, but there have been posts that it will get you into international C lounges, so my guess is that it would work. If you try it, please report back what happened.