PLEASE NOTE: use RG316 or RG178 coax cable with female RPSMA connector. This is per IBCrazy's recommendation. When you use the thinner stuff it just bleeds a ton of signal and you get really bad range.
UPDATE: It works great. Enjoy.
The other part like this suggests using a hacksaw and a dremel to modify the antenna hole on the top of the Taranis. I wasn't satisfied with this as it is much simpler to print a part that fits the existing hole.
Instead of a hacksaw, I used a flush cut saw which is much finer and cuts that plastic like butter. I used that to cut the two rings that remain after you remove the stock antenna, cutting down flush with the top of the case. This leaves a ring of plastic and a 9mm hole; half of that plastic ring is intended to slot into the other side of the radio case. I then made a cut along the seam of the case so as to remove that ring; after a line was cut I just snipped off the plastic with a pair of flush cutters and tidied it up with a razor.
When you join the cases, you end up with an opening which is comprised of a half circle 9mm in diameter and and the other side is ~13mm. This part is designed to fit in that slot perfectly. In order for the SMA connector to fit well, and for there to be plenty of thread exposed, I shifted the hole off center. There are two supports that fit the taranis case and support the antenna.