A picture of the place where you want the plant would be helpful for sure. There are plastic drian pans that could have a plastic tube attached at the drain and hidden behind the post but without pictures of the whole thing who knows.

If there's a hollow core in the column your best bet would be to pop the cap off, run 1/2" pvc to the bottom and elbow it out through the side in an inconspicuous spot. Drill out the cap and set it back on, trim the pipe, and set your planter. Only your hairdresser needs to know...

Otherwise, I've never seen what you're describing. I'd get a pan with the highest side walls you can get away with, drill it out for a bulkhead fitting, run 1/2 pvc and paint it to blend with the column using Krylon or something similar.

I believe THIS will work. You would need to attach your own pvc pipe.