Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:3493186.
I printed the original and found the airflow to be lacking in pull config. I get dry eye so I felt like it would be best if the fans were pulling rather than pushing. I made this one up and the airflow was increased so much I considered reducing the fan speed but in the end I was happy as it is.
My only complaint is that with headphones on over the Oculus you can hear the fan vibration, however I soon tuned it out.
I cut the holes in the facial interface in a similar manner to OP however I used a soldering iron with a chisel tip and removed all of the material below the air channel. I then cleaned up the surface and super glued the duct to the interface. Works a treat.
The space between the fans is large enough to house all of the original cable from the Noctuas (providing you are tidy about it) so I didn't have to cut the cable. I used wires with pins on the end to connect to the original connectors.
The switch is now complete, photo uploaded. Its tight, but it works! You can obviously adjust it's position simply by using different length cables. :)
P.S. The cooler in the photo didn't have any holes for screws. I added them by hand so only did 2. The model has holes for 4.
Edit: 25/03/2019 I found that the switch body on the side interfered with my headphones so I made a clip to attach it to the top strap, I also made a lid with a hole for the switch in case you wanted to install it there. I haven't printed it but I can't see any reason it wont work. You'll have to shorten the fan cables to fit it though.