You say that, and yet I've found more than a few UK breeders that just... breed their own rats for live feeders.
They way I get my kids to switch is, I offer what ever they were eating before I got them. If that means live, then it's live. If F/T mice, then F/T mice. Once they GET EATING and settle into a pattern I wait until they hit a shed cycle, skip feeding for that week, then offer whatever it is I WANT them eating the next week. They're usually hungry enough from the pattern break that they want to get right back into eating. I have yet to have one refuse this method, but establishing a consistent routine before hand is key.