I decided to experiment first with a random glass vase, in case the paint was not as peelable as advertised. I tried painting it with a brush, splodging it on, dripping it, and painting it thick with Brusho pigment. The front face below was the painted one.
And below: on the left, the poured version, and on the right, the thickly painted version with yellow Brusho pigment making the paint greener in places.
The swirls and pours were interesting, and as you can see, I was able to peel both the strips of paint above off the glass vase and stick them to the window, no problem. But it's pretty clear that the paint, though translucent when thin, quickly becomes very dark if applied a little thicker. So I decided the pouring idea was out, and instead, I used a brush (at arm's length!) to paint this:
It's quite cheery, and if I fancy a change of design in a month or so, I can easily peel it off and paint on a new one.