I am not commenting on OP situation. I am stating simply, "no thermostat with heat tape is high risk". Period. Now if you ask me, "Should I risk killing my snake by 53 degree temps, or by burning him, and possibly my house?". I cannot give you a real good answer to that question. Can anyone?
Furthermore, before one "rescues" a pet (any pet), one should be sure the situation they are bringing the animal into, is actually good for the animal. If you wish to rescue BPs with the only options being over heat them, or freeze them, I suggest you re-consider rescue efforts, until you have proper set-up. The OP asked the question about heat control, and we answered.
Good luck to you...and the poor snake