Here is my shower hand-mount. I used a free model and rigged it in Blender to make it fit my shower handle. Its 28mm x 150mm approximately. I ended up using a zip-tie so that it doesn't move as the handle would otherwise slip.

I can definitely be improved, so feel free to remix it!

The wall mount has two 4mm holes aligned vertically with 20mm separating them. In the blender file you can change the spacings to your liking. For that you'll need to activate/deactivate the bool modifiers for hand and mount to correctly export them as they relay on eachothers geometry… To export the hand > activate all bool modifiers, to export the mount > deactivate mount and all the screw bool modifiers from the hand

I would recommend printing the hand and the mount separately to print the mount with more wall layers and infill, as you are going to screw into the mount with the screws attaching the hand. 

here is a fun video i made for this