I would try to give the snake an air temp of at least 75 and preferably 80. That can be done with a heat bulb. You won't want it to touch the cage but putting it at safe stand off pointing at a side or through the glass will warm it up. You may even be able to get a warmer hotspot with a good air temp but you'll need a IR temp gun to dial it in to know the surface temps.

I would start with the light about a foot away and go from there moving it ever so closer to get things right. Go slow. It takes a a good while for temps to settle between changes.