In theory, you could get to the massage by taking the escalator up to the departure level (get past the escalator dragon by saying you are on an eticket and going to the international transfer desk). Rush through the massage. Go back down, and followed dsquared37's instruction from there

"When you arrive in BKK go to the confluence of A,B,C concourses and get stamped into the country. Collect your bags and go through customs in HKT. "

Note - you collect your bags in HKT.

In theory this should work, but don't know if anyone has actually done it or if it's worth the rush. If you give it try, feel free to report back here.