After it became apparent that there was no way my 12 y.o. would be able to drink all that contrast, we switched to the NG tube. They took us to an x-ray room and had him lay on the table. We gave him a stuffed animal to squeeze in one hand and I held the other. I stayed by the top of his head so he could see me. At first he didn't want to watch the x-ray monitor to see what they were doing, but after awhile he couldn't keep his eyes off it. They inserted it really slowly and when it came to the point of his gag reflex they kept having him swallow. After that, any time he got scared or didn't like the feeling, we'd tell him to swallow. This was a nice distraction for him so I turned it into a game. Swallow three times, count to three, repeat.
I believe the hardest/scariest part is getting past the gag area - just swallow, swallow, swallow. Once it was in, he could hardly feel it. They inserted the contrast into the tube with a syringe. Every time they refilled the syringe and started to push it through again, my son said it was cold in his throat and we'd distract him. Squeeze my hand, wiggle your toes, blink, etc.
Your son may be allowed to take the tube out himself if he wants to. After our last hospital stay, the nurse let my son do it himself and he liked the idea of being in control of something.
There are some videos on You Tube that you can watch of kids who insert their own NG tubes every night for nightly feedings. My husband and I found them interesting, but they freaked my son out.
The benefits of the NG tube... no nausea and they get all the contrast in that they need so the slides are pretty good.
Hope that helps...