Learning to drink while riding

I coached a guy a while back who always stopped to have a drink. He just didn't drink if the pressure was on - in races or bunch rides. He also wasn't interested to learn. He proclaimed it was dangerous.
In every novice group I've taught, there was usually one person who wasn't comfortable with the concept of having a drink on the pedal.
The first bottle cage I put on my Ibis MTB was a left-sided side-loader. It turned out to be a cage that no one likes putting bottles into, and for this right-handed rider who has never used a side-loader cage before it proved to be rather tough to use.

And then on the weekend I worked with a child who has good balance and riding ability, but strong doubt about being able to do new things (diagnosed ASD1, this child can be hard to teach). We made it a game.
Hover your hand off the grip.
Just for a moment.
Then longer.
Try to tap your nose.
Then try to smack your helmet.
Try to scratch something itchy (nose and ear were good ones).

Next progression was try to touch the bottle.
Try to grab the bottle.
Try to remove the bottle.
Try to replace the bottle.

Demonstrating the easiest pathway for the bottle to go back into the cage helped (not straight down the downtube of the bike, but on an angle that opens up the hole the bottle is going into).
The bottle fell a lot of times when it didn't get inserted fully. But we were riding in a flat area so it didn't matter that the bottle fell.
Finally it was time to grab the bottle, drink from the bottle and reinsert the bottle. This was achieved a few times.

At two points we broke away from the one-handed work to go try something else (specifically to break up the practice monotony). After a few minutes of trying other things, we came back to the one-handed pursuit. I returned a very happy child to a parent at the end.