I’d recommend liquid treats then. Meat baby food to be specific.
In my experience, just about every rat is OBSESSED with meat baby food, and they will do just about anything for it. Assuming that you can already handle the rats, I recommend combing the two (and even if they dislike handling, combining it with meat baby food is a great way to make it a more positive experience).
Basically, pick up the rat, then feed meat baby food of your fingers. (As a note, be sure to feed the meat baby food off a metal spoon first, to teach the rats to lick it up instead of biting it.) You can also work on lure them into your hand to eat it, or pairing touch with it.
The way I’ve always tamed and bonded with my rats has been outside the cage in a safe space, so you could also try that. I have a small and large cardboard playpen I build to free-range my rats, as my room is unsafe for them to roam around in. While taming, I set up my smallest playpen (just larger than me sitting cross legged), take my rats out, then sit in the empty playpen with either a blanket or hoody on. I also bring sling meat baby food to help cement this area as a good experience.
This way, the rats get to explore the area and learn to treat me as a safe spot. I’ll also practice scooping up the rats, giving them a lick of meat baby food, then immediately letting them go. This way they learn that being picked up leads to good things, and not to scary things like being restrained for long periods of time.
After my rats learn to tolerate and then enjoy handling, I switch to the large playpen. I add lots of toys and hides, and essentially just let the rats explore. After a while, they’ll end up near me again, at which point I’ll offer some treats. And after that, the rest is just repetition to accustomthem to my routine.
I’m also a big advocate of training small pets, and I train my rats daily. Spin, fetch, agility, weave walking, you name it! They love to train, and it’s a good way to bond with the less human oriented rats (and basically any rat in general). Each rat learns to communicate with me better, and overall they learn to trust that being around me and the play area is safe and fun!
