Most of the care sheets I have seen and in talking to people at Varnyard and from very new personal experience, ( I am sort of new at this), if you put ground turkey and liver 3-1 parts, and mix it with a food processor they seem to like it or at least mine does.
I haven't had a tegu in years but recieved one yesterday, a Red Arg. Yesterday was cricket day and today it was a scrambled egg w/ calcium powder for breakfast then he snacked on Tilapia for lunch. He is 18" by the way and he packing away the groceries. I also bought a slice of beef heart with I have heard they like as well.
Best of luck with your friend.