Yep, you did the right thing, wait until you get a thermostat to control the UTH to plug it back in. Correct, just rely on hot/cold gradient.
BPs burrow so this will actually be helpful. If the snake wants the temp right on top of the UTH it will dig, if not it will move some substrate around to get the temp it wants. And this is what you want. I keep mine at 91 and I have yet to see (other than my freaky fire male) any BP NOT dig down to get as hot as they can.
To get the temp with the digital therm you'll want to place it on top of the glass directly above the UTH, it will read just a tiny hair under what the actual surface is but close enough. Something inert thats not too hard to get off would be good to keep it in place. Something like hot glue or bathroom caulk without adhesive. The glue is better though as caulk obviously takes forever to set up you would only use it in a new set up that you never planned to remove.
