THey make a syringe that has a little "hook" at the end of it. Its used alot for people to irrigate their mouth after teeth pulled, anyway I use it and you can slip the plastic end/hook in the back/side of the mouth and push it down their throat very quickly and its too far back for them to spit it out. Go to a medical supply and ask them for one. they come in 5cc sizes and up. They good thing about it is they don't even have to open their mouths for it.
Good luck
