You didn't mention dynamite. (Only kidding since you're tried everything else.)
Since the windows are plastic, many options are out. I've used Skin-So-Soft with with cotton balls for this type of job. That's right. It's diluted enough for this use. And when you're done, windex cleans it up. You said you're tried gasoline; I'm surprised that you didn't mention that this ruined the plastic. Gasoline can do a lot of damage. In my opinion, never use it except in your car. If you're patient enough, you'll find ways (like posting on the WEB) to get an answer to what seems like a dead-end problem.
Perhaps using a hair dryer to heat up the glue will help. In case you don't already know, there are tapes out there for the type of job you needed to have done. It's called Painter's Tape. If you look on the INSIDE of the tape rolls, it usually says what kind of tape it is (as well as on the outside of the package before it's opened.) I have a number of opened rolls of tape for different jobs and if the inside of the roll doesn't have a pre-printed usage label on it, I write it on the inside by hand. Don't use masking tape when painting or staining. It actually absorbes the paint or stain!
I don't have much else to offer. My best to ya and if you need more help, post up.