1. The story said that agents "demanded" the guy return the device. Sorry, guys, you put it on my car, it's a GIFT, and you're NOT getting it back without a court order. Assuming I still have it at all.
2. Placing it on another vehicle is an idea that has merit. Especially if you can locate, say, the spouse of a fed.gov LEO. An anonymous phone call to said spouse could result in much hilarity, depending on what is said. (A message "accidentally" left on the "wrong" answering machine - ostensibly to contact the other spouse - is only one possibility.)
3. Transfer bug to a network news reporter's car or news van - think they'll run a story?