I have Sunpass here in Florida, and the newer version I have now does NOT work in my pocket or in my bag. I also thought of placing it on the brake reservoir, that would probably work just fine. Most of the toll roads in Florida are starting "Toll By Plate" so if you don't have the pass it just snaps a pic of your plate and either bills your account or sends a bill in the mail. You just have to make sure you license plate is registered to your sunpass account. I have noticed though, that on a motorcycle the toll by plate has about a 50 percent success rate. I think the cameras can't always get a clear shot of the smaller license plate. I've gone through at least a dozen toll by plates in the last few months, and I've only been charged for 5 or 6 tolls. I keep checking my account to see if I have any pending violations but so far no.
I use toll roads maybe once or twice a month, so unless I start getting toll violations in the mail I'm not going to sweat it.