It can be done. I have seen it done.
You'll want a larger species of gecko, the body length should be the same as the chameleon. I have seen pictures of chameleons eating each other and they were typical male/female sizes of adults (male eating female). I have seen an adult male panther chameleon kept with an adult male giant day gecko. You could keep larger species of geckos, nothing smaller than an adult Phelsuma m. grandis though, smaller species would become meals.
Chameleons may also shoot at food the gecko may have sticking out of his mouth, resulting in a gecko with severe skeletal hemmorage, or a very fat and very sassy chameleon.
Chameleons from Madagascar prey upon day geckos, as many species of both are from Madagascar, and thus a smaller species would just be a natural food source for a chameleon.
Goodluck, if you're going to try it, I'd advise just getting a gecko roughly the same length of the chameleon, and not too skinny.
45G screen upright vivarium sounds alright, but the bigger the better.
-Brock