1) I've never done it, but if you could figure out the right sugar ratios between maple syrup and corn sugar, you could do it.
2) However, I wouldn't do it, nor would I add it to the primary or secondary. You can place a pretty safe bet that unsanitized maple syrup is absolutely crawling with all sorts of little organisms that would just love to infect your beer. It's sweet, it's sugar, and wild yeast are sure to be all over it. But if you were to try to sanitize it, you would end up cooking out alot of the flavors that you're looking for. I'd try adding it after flameout, but past that...I'm not sure you could get away with it.