EZPass

Anybody out there using EZPass with your Prius? I applied for NY EZPass (cheaper than PA, where I live), filled out the form indicating that I needed one interior (for '91 Explorer) and one exterior (for '02 Prius) transponder---following instructions on info sheet, which I took the trouble to confirm by phone with NY EZPass service center. So naturally they sent me two interior transponders. Phoned them again, lady said she'd send out correct device right away. Received package the other day---total contents, two one-way screws (is this symbolic?), no mounting bracket, no instructions. So I'm wondering whether the stated reason for using exterior-mounted transponder, namely that the heat-reflecting glass in the Prius windshield prevents the transponder from being read at the toll gate, is really true? Also, for security reasons, I'd rather have the thing on the inside of the car, plus I don't really want to drill holes in the front bumper. My idea for an experiment is to head out to the Turnpike, go through the "EZPass and Ticket" lane with my trusty assistant holding the transponder up to the windshield. If it works, great; if not, I can still take a ticket. I'd appreciate hearing from any EZPass Prius drivers about your experiences. Thanks in advance.