unfortunately i have had experience with RI's and oral meds. what i have found works best for me and oral meds is to take the plastic ink cartridge out of a pen and clean it up. then measure from the base of your snake skull to the end of its neck, where is starts to get thick. press the plastic pen piece into the end of the syringe and make sure its in far enough and its tight enough that it wont come out and it wont leak. i usually fill it with water and plug the end and the push the plunger down to check for leaks. once it is clean and secured you can delived meds much easier. just gently slide the syringe down the snakes throat until the base of the syringe is in their throat and push the plunger down.
this is pretty easy when you hold ur snake just behind its head with thumb and pointer, and use the other three fingers to hold the snakes neck straight, when you gently slide the syringe down ur snake will starighten out with it. but you MUST be careful so you dont damage the inside. they do smallow rats with nails so the are tough but you still need to be carefull.
once the meds have been given, hold your snake with its head higher than its neck so the meda can run down and not out. i have used this method with two snakes many many times and it works very well.
sorry for the long post, just trying to share my experience
oh ya, if he starts to squirm you can hold his back end between your thighs or between your arm and ribs. i find it easier by myself but maybe an extra set of hands will help