In my personal experience I've found that heat lamps are way more effective for the ambient temperature of the tank than heating pads. I've noticed that heating pads stuck on the side of the tank only increase the temps by like 2-3 degrees, whereas the heating lamp can bring it up 10+ degrees. So I would say if you're worried about it being too hot, go with the heating pad on the side of the tank and maybe just try and keep the room as warm as possible until you can put him back in with some substrate?