Short answer: Just spend some money and get slider windows. You save yourself lots of time and trouble. Read the long answer for 'why.'
Long answer: My YJ has tinted rear windows. The way they do it is, they take the base clear vinyl when it is still a molten liquid and they inject tint coloring into it. It is then mixed for even consistency while still 'wet.' Then they let it cool, roll it, cut it into sheets and make the windows out of it. So the tint on the windows is actually coloring bonded with the vinyl. The vinyl itself was tinted like that before it ever reached the Jeep factory.
There is a way, but it's quite costly (it'll cost way more than slider windows) and will only last for a few years (and that's only if you don't get a lot of sun where you are, or your rig is garage-kept.) Static tint will stick but you need to buy new sheets of clear vinyl that haven't been stretched/deformed by the sun. Then, tint that. Then, cut it to fit and have a canvas/interiors shop replace the old vinyl in your window skins with the new vinyl that you tinted (this is the expensive part.) You'll also have to figure out some way to keep the new vinyl firmly taught while you apply the tint. Laying it flat on your garage floor won't work; it has to be perfectly flat and even. Otherwise you're going to get massive amounts of bubbling, and that never looks good. Finally, it will eventually start to look really bad as the sun hits your new vinyl windows and they deform from the heat.
