I mounted my MA EZ-Pass behind the front grill of my Model S, so I thought I would share my technique for other's benefit. As a side note, I hate the way that EZ-Passes look when mounted on the inside of the windshield, and I've heard that the coating on the windshield gets in the way of it functioning. Two quick photos of exactly what the MA EZ-Pass looks like. So you can get a sense of the dimensions. First I removed the section of the front grill/cone based on the technique detailed in prior posts here (using a credit card to pop the hooks that hold it in... quite easy) More detail of it coming off Here you can see that the transponder is too large to fit into the hole without sliding it behind the cone first. My first idea was to mount it on the back of the piece I removed, and simply replace the piece. But it was clear at this point that the transponder was going to be too large. So, my idea was to mount it to the piece I removed, but bump it out enough to clear the tabs that hold the piece I removed in the cone. To bump it out, I used a piece of foam weather seal that I had from an old weather sealing project. The key here is that it goes out far enough to clear the hooks that clip the piece into the cone. This way I could slide the transponder/piece combination into the hole, but it wouldn't pop off once resealed. I used command strip velcro to hold the transponder + foam to the cone piece. I did this so if I needed to move it up/down/sideways it would be easy (plus it gave me a few more mm of clearance). Here you see the combined unit. Note how the transponder is mounted "up" higher than the top of the cone piece and out ahead of the clips. This way it will fit up and into the space behind the cone. And, finally, here is a very hard to capture shot of the unit being replaced. I had to slide it "up and into" place, to keep the transponder attached. Hope that's helpful for anyone else who attempts this project.