A friend broke her leg fighting off a shark and needed a way to attach a water bottle to her crutches. We designed this in Blender and it worked out well enough that we felt it was worth sharing!
Should work on any 3/4" pipe and can be scaled to other sizes.
It may need slight trimming to get it to fit on the bar. Depends how flexible your filament is.

Sliced in Simplify3d with 50% infill (total overkill) and printed in PLA on a RigidBot.