My EZ-Pass tag is attached to my windshield or fly screen. I simply use the normal plastic velcro stuff they give you for my windshield and a combination of their fasterner and a wide strip of velcro down the middle from Home Depot on my fly screen because of the complex curves.
Years ago when such was a necessity for me through the front gates, I fashioned a small thin metal plate with a tab to fasten to the lower fender bolt(s) on the front left fork tube. It was inconspicuous except to the gate guards who work looking for it. Other riders stuck the gate passes to the lower tubes. A real pain to remove and damage to the finish was certain. Those passes you mentioned are unfamiliar to me. Hopefully they're not legal pad size