Yes, but it is a option that you can only make. I wouldn't, the main objective is to get him eating trying to "make something work" takes time, which is something that you might not have.
6 qt can be set inside the tank with 1/3 of it's floor on the hot spot in the tank. Put the probe in the tub and up the thermostat to get the hot spot in the tub up. No need to remove the uth when you can just use it where it is at.
Tub set up:
SSPX0192 by Mitsumike, on Flickr