Eddie, first of all, thank you for comfirming that the Vado SL handlebar remote would work with the Creo 2 system. Did you use the Trail Remote 2? Could you share more details how you did it and what the part number was?
Regarding the handlebar diameter: Any modern flat handlebars have the grip area diameter of 22.2 mm, so no issue to install the handlebar remote. As you correctly pointed out, the flat bar remote is a ring that has to be installed with all the left handlebar components (grip and brake lever) removed prior to the installation of the handlebar remote. You are also right to notice the road handlebar diameter is 25 mm, so the remote would not fit there. Did you use the T10 screwdriver to tighten the remote, Eddie?