Tim, have you gone to soflasportbikes.com to read any of their stuff? They have a thread about the toll cards in FL. Seems the cards work best when you are going about 20 mph thru the gate. Just an excuse to accelerate after! Guys w/sportbikes say they put it in their tailpieces & it works OK but you have to be going slowly for it to register. I'd say, do the legal thing so they can't get you for a toll violation. The state website says "these may not work w/motorcycles," but as-long as you can produce one if stopped, I think you should be OK, unless the L.E.O. is just looking to bust-balls on a "Spiker!":rofl_200: Also, in Miami-Dade Co. on the "Lexus lanes" (I-95 toll road lanes) motorcycles are exempt from tolls!
As to the obscured plates or movable plates, those are violations in and of themselves. They are just reasons to be pulled-over if a L.E.O. sees you w/one. You can buy solenoid-operated pivoting plate holders. Why would you have one? "Why, officer, to make it easier to change my flat tire when I pick-up a flat from the poorly-maintained roads!" Unless they see you w/it obscured/folded out of view, it shouldn't be illegal if it's rigidly-mounted, which the solenoid version should do for you.