I don't know about the whole " they do better on rats than on mice" thing. About half of my balls are rat eaters, the other half mouse eaters.
They all gain weight at roughly the same pace as long as I feed an adequate number of mice. Yes, it does get tedious feeding 4 or 5 adult mice as opposed to 1 rat, but to me I don't care what they eat as long as they eat!
I also want to point out I have 4 snakes who alternate between rats and mice, I let them have whatever they want. Maybe I spoil them, but they're my babies so I can spoil them if I want to.
I would much rather have consistent feeds, even if those are composed of 4 or more mice, than hit-and-miss feedings or outright fasts trying to force them to eat rats.
Now, about your snake. If you can get rat fuzzies, which are roughly the same size as a mouse hopper, and your snake will eat them, then by all means feed the rats.
However, if you can't consistently get the rat fuzzies, your baby will do fine on mouse hoppers and soon young adult mice.
Gale