Practice, practice, practice...
1 start out on a quiet rode (or parking lot)
2 glance down with both hands on the bars and then look at the road
3 just touch the bottle and replace your hands with you eyes on the road. If you can do this without wobbling around the road, move to the next step.
4 Pull the bottle out. Stop or toss the bottle in the grass
5 glance down again then back at the road, put the bottle back. If it doesn’t slide right in, glance again. Never let go the bottle unless you’re 100% certain that it’s in the cage.
6 with both hands on the bars, glance down again to make sure the bottle is seated correctly