To us this seems like torture for an indoor cat, but for an animal with the right temperament (not to mention owners willing to make the commitment) the Cat Veranda could be a godsend.
The Cat Veranda is a window insert with a flap on the interior side and a mesh cage that juts out of the window. It's shady and carpeted, but we could see putting a little bed in there to make it a bit more comfortable. Our main concern, though, would be security, both from intruders and against the likelihood of the contraption falling out of the window with our cat in it.
• Cat Veranda from PetSafe