This is a great video on how to syringe food or meds. I would do a small amount at a time so it coats their mouth without being enough to spit out a significant amount, since that would make it harder to dose accurately. If you have trouble, measure out one dose and then mix in some fruit flavored baby food (banana is a nice strong flavor to help mask the meds) before sucking it into a syringe (which you can buy in the pharmacy section of any store).
That's true, I didn't think to ask because I haven't had dogs in a couple decades so the concept of preventative worming didn't cross my mind. The others are right, that's not something one normally does with rabbits.