I have to admit that I've never converted a snake of this age from live to frozen/thawed. I did do it with my younger BP, and he now takes them like normal (only a few months after I bought him).
I recommend feeding him one or two live meals, until he's settled in and comfortable. If you can stand to kill the mice at first yourself, you'll have more success in my opinion. Kill an appropriately sized mouse or rat, I just put them in a grocery bag and slam them onto a hard surface, my bathroom sink. Don't pulverize it, just kill it. Take a pair of long tweezers or needlenose pliers and dangle the warm mouse in front of the snake, hopefully he'll strike. My snake does this readily. After two dangled warm meals, you can probably just put a warm mouse in the hide box, do this for two meals. Then you can just start feeding thawed mice and I expect he'll take it.
All of this will take pacience and what some might consider cruelty. You may let him miss a feeding if he won't take it, instead of breaking down and giving him a live one. My snake did this only once. Anyway, I hope it works out for you. Post us about it if you do get it.
Taylor