I try to use up my old detailing products that I have found better ones for on this type of thing (or as a member of another forum used to say, using products from my "Disgraced Products Shelf"). I have almost used up my circa-2003 bottle of Meg's Gold Class on the aluminum exterior cladding of my windows and doors, and my patio table.
But getting back to windows, I used to use Clearkote Vanilla Moose (not a disgraced product) on my windows. It was quick and easy, and kept the windows cleaner than not having anything on them. I would think something like AquaWax or another spray wax or sealant would be an easy way to do this. Meghan's suggestion of the Klasse twins would work well, also, especially since it's so hard to use up a bottle of SG!