When you do assist feed what size prey are the neonates eating? I don't like assist feeding pinkies (whether mice or rat, depending on neonate size) because they're basically just squishy bags of water, and trying to force one down a snake's throat makes a gross mess. Instead, when I assist feed I start with something like the hind leg cut off of a f/t mouse or rat, followed by a whole prey feeder of appropriate size unless the snake is so tiny that the hind leg is a good sized meal on its own. Otherwise, the hind leg should be sized so it's a decent mouthful for the snake.
Have the warmed hind leg and whole prey f/t feeder ready to go. Grasp the snake's head with your thumb and forefinger just behind its eyes, but gently around the jaw so that it can still open it's mouth. The snake's neck should be supported by your other fingers.
Take the hind leg and fold it at the hock joint. Insert the folded end of the hind leg into the snake's mouth. This is easier than using a whole feeder because the long leg bone is perfect for prying the snake's mouth open. Push the hind leg back as far as you can into the snake's mouth/throat.
The hind leg is very hard for the snake to eject since it will unfold and often gets caught behind the snake's teeth when the snake opens its mouth to spit it out. The snake will likely try to run away while attempting to spit out the hind leg. That's fine, just let it run through your hands. Sometimes the snake will also try to scrape the hind leg out of its mouth by rubbing it on its own body or your fingers. Try not to let it do that.
When the snake stops running and starts swallowing the hind leg, quickly sneak the nose of the whole prey feeder into the snake's mouth so it follows the hind leg down the hatch. You may have to support or push on the feeder a bit but the snake should grab and swallow the feeder once the leg moves down the snake's throat a bit.
Using this method it takes me about 10 minutes to assist feed each critter so hopefully that will help.