railing idea
If you can find one with others not leaning on it, or walking on the supporting structure....
I have a large A clamp... the sort that I have littered around the studio space to hold flags, refectors etc. I have a 1/4 -20 stove bolt drilled into the back side, with a wing nut on it. You take the head off of a light weight tripod, and thread this thing onto the head.. Bingo. Camera support to go that fits into the tripod. It works well in zoos etc that als don't allow tripods. Zipp it all unassembled into the camera bag. Clamp it onto the pole that says don't feed the animals, etc, and you have a great steady platform to shoot from.
It is not quite as stable as bolting a tripod head onto a Manfrotto super clamp fitted with a 1/4-20 stud, but it is also about $80 cheaper.