I had the exact same problem a few years back. There is no easy answer, but I would encourage you to look at other things besides a wire. There are many cheap "apartment dweller" antennas that are verticals - some with coils and some without. Unfortunately every antenna will be a compromise in your situation, but look around at "mobile" or "Travel" antennas, find one that looks like it will fit into your setup and give it a try. Most are cheap enough that if it doesn't work you can order another type without too much hardship. Again, beware of wire setups in apartments - kids love to pull on wires, and landscapers like to cut wires. Also, make sure that you have an excellent ground. you never know what the building was built on. Best of luck,
Jim