I also found a giant suction cup (intended to hang heavy wreaths) that after 4-5 attempts actually stayed stuck to the window, so I hung a birdseed bell from that. I may pick up another one or two of those suction cups to attach birdfeeders to other windows. The more I have, the more places the birds have to eat when the cats are skulking around the hopper.
I want to get a large over-the-branch hook and some rope to see if I can devise a better way to hang the big fly-through feeder. It's currently secured between two branches with string, and not as secure as I would like.