Some hatchlings do poorly on rats and some do poorly on F/T, I know it's not what you want to hear but what I would do is offer a live rat and see how it goes and than once a little better established convert to F/T again.
Worse case scenario if that does not work, live mice.
Some will convert to f/t very young, some will take a rat as a first meal and some just don't.
The bottom line you need to feed what works because assisting is just not a long term option and is detrimental to your snake's health.