i had this same problem. how i did it was i attached the probe directly to the UTH from the old set up. (i dont know if you have it already set up like that or not but i like to keep the probe on the inside of the enclosure.) set both tanks next to each other on the floor somewhere close to where the final enclosure spot will be. then when your new tank gets to the right temp or close. quickly switch the probe over to the new tank. make sure when you make the switch your snake isnt in its enclosure. temps could change fast and hard. then just make the little final adjustments with your snake on your shoulders