At the moment when I had to clean windows which had limescale, bird poo - eggs and so on I used my squeegie on the end of the pole and applied a detergent to the stain, the problem though was the squeegie was to soft and you really needed to scrub the glass.
Anyway while shopping at sainsburys I saw a new product that Vileda have brought out, it is called the Bath Magic 2 in 1 mop.
The head screws off the short pole that comes with it (you can use this for downstairs windows that are difficult to get to with a normal pole) and will screw onto your pole if you either remove your brush head or have a separate pole.
The head on the mop has a sponge pad that comes off if you need to replace it, or to change the pad from a sponge pad to a blue non-scratch scourer for stubborn marks.
I used it last week on a building that had bad linescale on all the windows and it worked brilliantly, it was faster and easier than the squeegie.
Sainsburys sell them for £6.98 you might get tem cheaper elsewhere though.