i've read that comment before, and it really isn't tough once you get the hang of it...
this is for juvie and adult sized snakes, and not for oral injections 
NOTE TO ALL BEGINNERS: MEDS ARE LIKE PROBING A SNAKE. IF YOU HAVE NEVER DONE IT, IT IS BEST TO HAVE AN EXPERT (A VET) SHOW YOU FIRSTHAND A FEW TIMES. YOU CAN SERIOUSLY HARM YOUR ANIMAL WITH YOUR IGNORANCE, SO DON'T GET IN OVER YOUR HEAD TO SAVE A VET BUCK, LEARN PROPERLY BEFORE YOU MEDICATE OR PROBE!
load you syringe, and have it within arm's reach of the front of the cage. grab the blood, and pull it out of the cage. hold just past the mid body, let the head go back in the cage, and the snake will pull itself pretty taut. you are going to inject under the wider scales just off the side of the ventral scales, 1/3 down the body. as the snake tightens up, and is trying to get back in the cage, tighten your grip a bit to slow down progress, spot your injection point, and then slide it in, and shoot it up.
if the animal gets too far in the cage, i just pull it back out again, to the head, and pinpoint my 1/3 spot again. Vision cages (and many others) have a nice lip to the cage, whether the front or the lid, and once the snake gets their head around the lip, they use it for leverage to get back in the cage. they will have a very difficult time striking from this position,and their main objective is to go AWAY from you and fully back in the cage.
best of luck!
-----
robyn@proexotics.com
Pro Exotics Reptiles