Ok since I am the "Expert" in screw removal there are a few things you can do EXCEPT what them guys above are recommending!
1) Make sure your Allen Key isn't worn. Major cause of rounded allen screws.
2) Get an e-z out from the local Automotive Shop that fits that allen tight so a tap of the hammer will seat it. That will do the trick.
3) If all else fails come to Suffolk and pay me some beer and I will make sure it comes out without damaging the Marker!