EZ Pass recommends you put it in pocket on jacket. They don't want them left on bikes in any manner they can be easily stolen. I always wear high visibility safety jacket or shirt when riding, if you do that remember the reflective strips are often Mylar, which can block the signal from the pass. Learned that the hard way of going through booths and having sign say it was not read.

That said you can go to a marine supply and get 1" plastic clips for attaching stuff to railings on boats. You can easily get an EZ holder and attach the clips so it will clip onto handlebars.