I wonder why Feld don't make more solo variant of his games. I would love to find a solo variant of Aquasphere, Bruges or Trajan (maybe with a dummy player deck of cards or something like that). I own a lot of games and my group tend to always go for the new one and I sometimes want to enjoy a game but the schedual is not good to everybody. Solo variant is also fantastic to revisit the rules of a game you did not play for a while.
I've made variants for a couple of those games, and there's a very good, simple one for Castles of Burgundy. Just check the "Variants" section of those games' forums.