I rarely have peanut butter in, but when I do and give it to the girls, I give it them on it's own... neat peanut butter!! haha but I make sure to only give them tiny tiny TINY bits... WAY SMALLER than a pea, as their choking's made worse by how greedy they are and how fast they shove it down their necks.... it you get a weeny bit and spread it all over your finger, this makes them lick it off and stops them getting a big, chunk that they try to gobble, getting stuck in their throats.... also don't give them a lot at a time because larger amounts are obvioulsy more likely to clog them up, line their throats and stomach and make them choke.
So yeh, I just give my girls tiny tiny bits, and they don't get them very often really... Their usual treat is mashed potato that has a diddy bit of cream in, or maybe a bit of macaroni cheese.... I don't need many treats though, as Jiggs loves her cucumber and the babies love grapes! So they can eat them all they like!
If you want to give you rat's more peanut butter as a super treat, you could try mixing it with warm milk... this smoothes it down a lot!! and stops it being so claggy. i just give them tiny bits though then they don't choke, and they don't eat as much and get fat! hehe Porkies