Update 2019 Aug 15: I was contacted by nichenke who tried to fit this on the Wahoo Elemnt and it didn't fit. He tried to modify the original design from the F3D file but it didn't update right. I tried and got the same results. I've found my new mount works better anyway, so I uploaded the longer low mount for the Elemnt with the new, better performing interface.
I work for a Trek bike shop, and got exposed to the Bontrager Blendr mounts and became an immediate fan. You can use it to mount various things to your bike without the typical clamp or series of rubber bands around the bar or stem, so it results in a really clean look to the bike. I've mounted a Garmin GPS and one of the awesome little Bontrager Ion 100 front lights to my bike without using up any space on my bar or stem, and it looked clean. That was all well and good when I had a Garmin computer, as Bontrager makes mounts for the Garmins. When I got a Wahoo, however, sadness ensued as there is no mount available for these great little computers. Folks on Trek University (training for folks who work with Trek stuff) asked for these mounts as well, but got no reply as to if Bontrager would release them, so, as always, 3D printing to the rescue!
The mount I'm happiest with at the moment is the "mid mount" - so called since it's about in the middle of the mount, vs. the Bontrager low mount and the high mount. This prints with minimal supports (and can survive no supports if your printer is well configured) and fits very well. The mid mount is designed for the Elemnt Bolt - I don't have access to a Wahoo Element to take measurements but I do know it's larger and might not fit the mid mount. If anyone can give me an idea of how much to increase the length for the Elemnt, I can adjust and make those versions available.
The high mount I created in case someone wants it, but it'll require a bunch of supports and I haven't even printed one yet.
I've listed Bryce's Garmin Stem Mount as a source as he modified his design for the Wahoo, and when I discovered it needed some adjustment, I used his as a template for redesigning from scratch. Yes - there are many Wahoo mounts I could have used, including this one which is even modeled in Fusion 360. The design is simple enough that I figured I'd draw it up from scratch, and I found in my early prototypes some adjustments which helped the design work with FDM printing.
Finally, why are vowels being dropped from both Elemnt and Blendr? Are they expensive? ;D
As you can see from the photos, prototypes were printed in a bunch of different filaments, most of those were PLA. For my final prototype, I used ABS for durability and heat resistance. Just about anything will work, although PLA probably won't hold up in a high heat environment, like inside a car in the summertime.
I always try to design to minimize supports, but they're pretty much necessary here. For the mid mount, they're only really necessary to support the lips of the mount itself. For the high mount, you'll probably want to combine a brim with a bunch of supports. You could try flipping it upside-down, but then the surface finish of the face of the mount would probably suffer.
I also had good results running these prints at higher temperature to increase the layer adhesion, which is really important for the two little tabs that hold the computer in place once it's installed. I found angling the sides of the tabs pretty dramatically (-40 degree draft angle) helped keep them from breaking off, which happened on several early prototypes.