I would say if you can reach far enough, using a microfiber towel and bunching it up should fill in that tiny area you can't reach with your fingers. If you can't even reach that far then I'm not sure.
As for cleaning the inside of the windshield in general, the best thing that has worked for me is a microfiber towel and Invisible Glass cleaner. Windex and the like doesn't clean it at all.