Not possible. You'd have to cut the railing to get it to resonate at the proper frequency, add insulators between the railing and its supports, and you'd get crappy performance because the railing is horizontal rather than vertical.
You'd piss off the HOA for an antenna that works poorly.
or you could run a coax to it and use a antenna tuner but risk getting into every ones electronics,,,,,there always is a way but it would be just a compromise ,,, there are antennas designed to be used on railings but none will be efficent,,,,
Never say never...We use to load a window screen (it was metal) with a 100 watt tube transceiver and an antenna tuner from a tank and talk to Germany on 20 meters from our 8th floor dorm room. There are several problems though.
1. rf burns if anyone touches it
2. very directional, the building will act as a reflector behind the railing.
3. with 5 watts you would probably be better off with an antenna made for limited space
4. more than 5 watts on 11 meters you run the possibility of all types of interference and distortion.
I'm afraid that no matter what you use if the antenna is not above the building # 2 will affect you.