To hold the part in place at the back of your Wahoo you will need 4 M2x6mm plastic screws. These screws self tap in the plastic and neither go totally Through the casing nor fail (at least after a year of heavy use). Do not over tighten them, if you do it the screws will loose their grip.
You can also use two zipties as backup in case the mount breaks.
The part should preferably be printed in a material with good mechanical properties, I used ABS and PETG with good results.
In my opinion this solution is superior to glued on add-ons, glue can have similar performance but is variable depending on the user, type of glue used and parts surface characteristics.