Years ago, I had oral surgery and had to have my jaw wired shut for a couple weeks. They gave me this thing that basically looked like a big syringe with a rubber tube on the end instead of a needle, so that i could squirt puréed food into my mouth. Then years later, I tried using it for rectal administration and it worked great. I highly recommend using something like this for plugging instead of a syringe. It's reusable, it holds more liquid, I find that the long tube makes the process of administering the stuff easier than with a real syringe, and depending on where you live, it's a lot easier to get ahold of one than a syringe. Plus, I'm always afraid that there might be a little bit of the needle remaining after i remove it, which i imagine could do a lot of damage!
Anyway, I guess the mods don't like it when you post a url in the forums, so I'll just say that if you want to order one, just search for "enteral/oral feeding syringe." Happy plugging!