Not sure where you live, but, in the accessory areas of the bigger carwashes and at some of the rest stops on the PA turnpike, they have suction cup mounted ezpass holders that you could mount on the inside of the windscreen.
I just leave mine in the glove box, put 'er in neutral while coasting into the toll plaza, hold it up, then put it back in the glove box while still coasting. Was a little awkward the first couple of times, but, now it's no problem.