I've had to do it, but only with a tiny baby who otherwise was likely to be in trouble - and that was only after i tried every trick in the book, and assist feeding stopped working. After about a year of this with only frequent enough forced meals to keep him healthy (not gaining weight at all), he took a mouse on his own and is a reliable eater today.

It was pretty much the most stressful thing I've ever had to do as a keeper, and I hope to god i never have to do it again. I've seen some larger snakes that look like they could stand to have a meal or two stuffed down their throats, but i wouldn't want to have to wrassle them for it, and i'd be very fearful of causing injuries.