I do this too, I roll up fist sized balls of chicken breast, lean turkey and beef liver then freeze them for later use. I'll sometimes throw in a few pieces of fruit, when I have it on hand for other animals, but seldom offer anything but meat to the tegus.
Those temperatures wouldn't be so daunting to a larger tegu. We often get days in the upper 90s, low 100s and mine do fine with an underground hide. I don't even bring them inside to overwinter until we start getting freezing temperatures - though by that time they have been sleeping several months already.This year I'm going to do an outdoor pen to keep it in during the warmer months or even on the warmer days. I wouldn't trust leaving it outside overnight with racoons, opossums, cats, etc. Plus we could have a 80-90* day but then the night temps drop to the 50's.
Boon is 3 this year, T. merianae is by far the most rewarding species of lizard I've kept!John how old is your tegu? I love the jowls on these guys, they're so squishy looking haha.