UPDATE: For anyone without access to a 3D printer, you can now buy V3 from Spencer on his Etsy store: http://www.etsy.com/shop/3DPrinterSpencer
Update 5/21/2017: Added a new version (V3). I think it strikes the best balance between size, comfort and easy reach to shoulder buttons. I also updated the screenshots to easily see the differences. I included a split version of V3 for smaller printers.
Here is a great video of V3 being printed by ModBot: https://youtu.be/8MzNG5oqPlI He goes over what print settings were used and what it feels like to use it with the switch. Thanks, ModBot!
Update 5/4/2017: Added two new versions (V2A and V2B whole). Some people mentioned it was difficult to hit the shoulder buttons, so that inspired me to try and fix that in the next version. I ended up making one that was really compact (version V2B) and thought I need to make one that was in the middle ground (V2A). Check out the comparison screenshots.
When you use the switch in portable mode for extended play sessions those hands start to cramp. I aimed for an Xbox style set of grips for the system while in portable mode.
I took a previous model of a controller by ant385645 for the shape of the grips.
I included a split version for smaller print beds but keep in mind you might have to sand the connecting rails a little to make them fit. I would recommend getting the whole version as it will probably be much sturdier.
Make sure you print the whole thing (or all split pieces) standing upright so the support material is only on the bottom faces and it keeps the slot part for the tablet as smooth as possible.
Make sure it is printed standing up right like in the first picture. If it is printed face down, the slot will not be wide enough (because of sagging) and you'll use a lot more support material than needed.