If kept properly, or even somewhat close to properly, you need to shoot them to kill them, or go to a bad vet. If kept in conditions allowing proper digestion and proper use of what food is taken in they do better on all rodents than anything else, period, and its proven. The problem is again I stress the point improper husbandry by someone who bought a $5 disposable pet on impulse beacuse it would be cool, I help work a bit with a reptile rescue, the only one in the state of PA, and a few friends are wildlife rehabbers that also take in abandoned pets outside of dogs and cats, they see the same thing, yet why cant my friends 4 bosc monitors get fat at all, they burn it off, and they are by no means kept in a big enough cage but he does what he can with alot of animals, and his eat many FT rodents (large ones) a week. Impactions, and obesity are husbandry problems, due to temps, dehydration, etc not to due at all with whole animal foods, this is proven everyday by those of us who have kept monitors for years and years, as well those who breed them. The insect diet for boscs is like use of UVB lighting on captive reptiles , a bandaid to hide serious husbandry problems.
By the way fowl (chicken peeps, and quail included are very inexpensive, as a matter of fact .10-.25 each for chicken peeps, and quail are a bit more, rodents are alot more, even hissers cost more to buy than peeps.
I personally use rodents (mice , rats), peeps (chicken, quail), and hissers, and lobster roaches as well crickets with my monitors.