Have you ever tried that Windex window cleaner for outdoor windows? It's called Windex Outdoor All-in-One. It's made for outdoor windows, but I'm pretty sure you can adjust the water level so you don't get so much water inside the studio and it has an extension pole with a windex-soaked pad on it. It really leaves a spot-free finish and as long as your stained glass window is not TOO fragile, it should be okay to use. I use it on my outdoor windows, even though I have a ranch style home and don't need the reach. Works wonders! Hope this helps. :)

I would invest in either a ladder or a long pole - or both. The idea of shooting water up at a piece of stained glass sounds like a bad idea.