After seeing your video of your scrambler, made me want a Triumph even more. Just hesitant to get one cuz I would have to park it in the same community garage that my ruckus got stolen from.
Not sure if you figured this out or not but Honda engineers have made the connector just small enough to fit through a box end wrench so you can take it off with one of those. A regular flat one.If you go over to Amazon and look for "12mm O2 Sensor Port Plug" there are a few options, and all pretty cheap. You need something a little bit wide lipped since you want to prevent any kind of air leak, so going with the sensor plugs you'll be fine. I'd remove all of it since it won't be used (and unsure with having it plugged in to the harness with the AF-1 would do since you'd effectively be getting two O2 readings). If you trace the wire from the O2 sensor up you'll find a small connector (just above your exhaust near the muffler) that you can disconnect at least to get the stock O2 sensor from sending signals. Removing the stock O2 may be a bit tricky just because it's recessed in there, so you may have to look around for something you can get in there to remove it (but don't bother until you have a plug).