Spot on Peacoat - what to do?
I'd recommend against that, I tried it once on a much cheaper garment, and the result was probably worse than what I started out with. :) Sharpies are definitely a bad idea.
A dry cleaner might be able to do something for you, or if all else fails, just have elbow pads sewn on by a tailor. It might actually look good, and might come in handy if the elbows get significant wear.
(Though my first experiment would involve a warm soapy towel. Maybe it's just whitewash from leaning on a wall or something similar.)