I agree with splitting the doses. We tried the "masking" method with the medicine Cabergoline, and that was a fail. Forcing often soils them on it alltogether (rats are so smart and stubborn as we know).
I've heard of people having success making medicine balls with rat safe cookie dough, and mixing the medicine in. Our vet suggested mixing baby food in a similar flavor to whatever they added to the meds (usually cherry or banana) to the dropper with her meds vs trying to just get them to eat it.
We however have just had to split up the doses and do our best, since thats been the only effective way. I'm sure you know, but you just wrap them in a towel as best as you can, head upright to prevent choking, and try to fit quickly and gently between the back teeth. We don't force it though and try to be patient until we can get it in her mouth. Then release it slowly (obviously not TOO slow, but gentle).
I'm not good with patience, but it's the only way for us.