CP is the best option for puffers, and also works best in a NON-CYCLED QT, as it can be degraded by a working bio-filter. Prime can be used in conjunction with water changes to manage ammonia. Just remember to re-dose the water in the bucket accordingly with CP before it hits the tank.
If you get the 110g up and running in the next 14 days, you can move your velvet survivors over and transfer the puffer out of the first tank and into the other QT with working bio-filter. That would be the best plan, since CP can be an appetite suppressant and it will be more difficult to keep it at the appropriate level as the bio-film begins to form.
After 2-3 weeks of observation he can join the others in the 110 if that is the long-term plan, or you can break down and sterilize the 55 for him... set it back up with live rock, etc and let it cycle for him.