I think it is fine to divide the large doses, but you need to do it with a small syringe so you know exactly how much is getting put on each animal.
Just look on the boxes and see what the dosage amount is for your animal, and you will know how much you need to put on each animal. You will probably have to do some conversions though, so make sure the check the math carefully.
I am under the impression it is ok to do this because the vet tech at the Humane Society I foster animals for has had me do this when they were out of the correct size for my foster animals. They did the math, wrote down the doses, and gave me some small syringes to use. I just dumped the Frontline in a disposable cup and sucked it up in the syringes from there.