This all depends on where exactly you are located.
Many States have laws prohibiting smoking in any building the public could access.
You say you work in an 'open office'.
What exactly do you mean by that phrase? A wide open floor of a building, with cubicles? A public building that allows anyone to come and go whenever they please?
Perhaps you could simply type an anonymous letter and leave it in his office, or slide it under the door.
Does the office he resides in have a window that can be opened? Might be a good start... "Open the window!"
Is there air conditioning connected between that office and the rest of the building? You may be able to get one of the facility personnel to make a statement.
You may be able to take a photo of him smoking, print it, and leave it on his doorstep with the words "You are breaking the law" or something similar?
I apologize for this, as I feel it is too 'passive aggressive' for myself to do.
I would sincerely ask the manager to cease before being responsible for my medical bills; include a copy of your actual doctor bill to show it is a valid issue and you are not just trying to cause grief for the fun of it. Also make sure to do this where other employees can see but not hear you. If the manager does anything incorrect/rude/obnoxious/unlawful repeat back what he said loud enough for everyone to hear. Unless the manager mentions it, avoid commenting about the the law in relation to the manager. It will definitely be a hot topic.
This answer may not be acceptable for you, but it is what I would do.
And my last suggestion if the others aren't acceptable:
Public building? Invite/Call/arrange for a few city people to come in.
Or school children.
Or your neighbor.
Have them begin the fight for you.