[Hocrest]

It will work, I've seen people hold them out the side window and out the sunroof, but...

I'm pretty sure you can be fined for using the EZPass in a vehicle other than the vehicle that it is registered to. I have never heard of anyone actually getting fined, but since it really doesn't happen that often, and there is no cost savings by using the EZPass, I'm not going to risk it.
That's the reason I don't borrow the EZ from my Legacy to use in the SVX or Brat. If they changed those rules, WooHoo, please let me know. I would love to move that box from car to car.