Don't do anything that could be a fire risk !! lol
Its easy. You can use an uth that's a bit bigger so it covers half the bottom of the tub and goes up the sides aswell so pretty much half the tub has a heat source.
If it's too cold you can use 2 uth. OneOne on the hot side to keep the temps about 32°c and then one on the cool side keeping the temps about 25°c . Will have to use 2 thermostats for that then thought.