I have had the tag registered on my bike for about 2 years and the thing is in the drawer at home because I sure don't want it on my bike either. I call once a month and have the zip cash converted to the tag rate. I talked to a representative about it and I was told that they charge zip and also if you are going over 85 mph they will also charge zip no better what you are in or are riding. Can always cover the plate with a tour pak if you have one otherwise we are stuck with zip if its not mounted.
I have never asked if its mounted on the rear of the bike if it would be recorded. They snap a pic from the rear and I did my own plate relocation and painted the top of the tail light, maybe that could be a place for it to be applied. All in all, it a rip off because most of the time if you are driving the toll roads, so is everyone else and you will end up at a stand still. Perfect world would mean no toll roads.