Another thing you can try is to feed a small rat first. Then about a half hour later offer a frozen thawed. Even my picky eaters will usually eat a frozen thawed right after a live one.
Also, be sure to have the rodent at the proper temp. One that is frozen on the inside but warm on the outside can be lethal to your snake. And if the temps are too hot or too cold they will go off of frozen thawed and it will be hard to get them back on. What I do is thaw in a fridge overnight and then an hour before I'm ready to feed I put it in an incubator set to 110F. Works great. For bigger rats you may want to incubate 1.5 hour or so, just feel the rodent and it should be warm to the touch. If you incubate too long they tend to get a bit 'off'.
You can also start with fresh killed. Get a CO2 tire inflator, some valve stems, and a small Tupperware container with a locking lid. I actually prefer to feed fresh killed, I don't have to wait for rodents to thaw and warm up and I never have to worry about them being the right temp or biting my snakes. They also seem to like fresh killed way better than frozen thawed, at least for a few of my picky eaters. Also, with fresh killed you can also freeze if they don't eat it and treat it as a frozen thawed next time. I never refreeze a frozen thawed, just too risky.
You could also get a big cage or tank and keep several live rats for an extended period of time. In my 40 gallon critter cage / glass aquarium with screen top, I can keep about half a dozen live rats long term. If you need medium rats you could get them on the small side and keep them for six weeks or so and by then they shouldn't be too big for your snake. Another option would be to keep a male and female pet rat and breed them, use some of the babies for your snake and sell or freeze the rest when they get to the right size. Just have to be careful that you don't get attached to the little buggers to where you can't feed them off or CO2 them LOL.
You could also do what I'm doing right now as I wait for my breeder feeders to grow up, I'm feeding a mixture of live and frozen thawed. I go back and forth depending on how big my feeders are, if they are too small I'll feed frozen thawed until they grow up a bit.
By the way, I use tongs and just hold them in front of the snake about two inches from their head. If they don't eat in about 60 seconds I move on to another snake. Sometimes I'll wiggle them a bit or lightly touch it to the side of the snake. And if they don't take it you can try putting it in with the snake, I'd say for no more than an hour or so. After that the rodent gets too cold for the snake to be interested.