I have switched plenty of adults that were only fed live to ft. And have only ever had 1 that took me about 2 years to get totally switched so I think with enough time any snake can switch. Sometimes it's easy, sometimes it takes lots of patience. And sometimes lots and lots and lots of patience. There were already lots of good tips listed so ill just repeat some if it that has worked beat for me. Thawed, dried (or mostly dried. I just use warm water then dry in a paper towel as much as possible), held with tongs at back scruff so its in a normal position and not just dangling, wait until night time and keep room as dark as possible so you can just see what youre doing, make as little disturbance as possible opening the enclosure. I have the best luck if the snake is in its hide to start and not out cruising around. It seems if i put the rat in and just sorta put its head by the opening to the hide that the snake is more likely to just quickly strike without having a chance to see that the rat isn't quite moving naturally or my hand in there with the tongs. After it strikes don't jerk back but keep the rat on the tongs or if it slipped off just use the tongs to grab a leg or something sticking out and continue to give the rat a little wiggle while the snake continues to wrap harder. It helps the snake think it was live and fighting back a bit like they're used to otherwise I've seen some strike then let go when the realize something is off. If it's in good body condition and used to monthly feedings then I'd just leave it totally alone and NO handling for at least 2 weeks before offering with that procedure. Good luck and don't give up if it takes a couple months for him to take one. Unless he's skinny then he'll be fine to really work up some hunger.