Illinois IPass Tollway - Mandatory Transponder Replacement

We used to travel to Chicago routinely when we lived in Milwaukee. So we got an IPass transponder probably fifteen years ago and have been using it ever since. A couple weeks back we received a letter from the Illinois tollway that we had to replace our transponder because it had reached the end of its expected service life. Since we don't live anywhere near Illinois and don't plan on visiting any time soon, I called and asked if they could send us a new transponder. They said they would only if we sent the old one back. I'm not exactly sure why we need to send it back, but I will. The new one arrived in the mail yesterday, saying it was already active and ready to use. But before I got rid of the original one I wanted to make sure the new one worked. So after brunch today, we got on the IPass and tested it.  Of course it worked, but one never knows! The only problem we have is that we cannot stick it on the windshield because of the eye-sight safety feature cameras built in the rear view mirror. So we need to hold it up as we pass through. I'll need to check with Subaru and see if there are other options. You would think there would be a better solution. Since we don't need to use it that often it's not a big deal. But I'll make sure the transponder is kept in a very convenient place. It's not something you want to hunt for at the last minute on a busy freeway!