Here's my f/t story for ya in a nutshell...
All of my snakes were on live prey for the first few months. Then my collection grew pretty rapidly and it became an inconvenience for me to feed live. F/t was really my only alternative being that the store I used to go to went out of business
Anyways, out of 12 balls I would say more then half didn't take the f/t conversion easily(9 to be exact actually). I have a pastel male that made it hell for me but from his stubbornness I feel I can convert any snake lol. What I did was instead of fighting it, I gave into his spoiled behavior. For a month(a little long maybe) I regularly fed all the problem snakes live. I got them on a normal feeding schedule, and by doing this they all displayed normal hungry snake behavior consistently the whole time. So for fun one day after my f.t rats were thawed for my other snakes, I decided to see if one of the problem feeders wold take it. Not only did he take it, but every last one of my snakes took one that day. I don't think thats coincidence.
What I think happens is if you can get them on a schedule for a least a month with live, and then try it I feel they just go for it rather then inspect it. Make sure its really warm. I notice some of mine won't take it if its luke warm. So I just usually just run them under the hot tap right before and they take it every time. F/t can be frustrating, and some snakes are more stubborn then others I guess you gotta see what works for you. Good luck!!