Rember PSN user DimmuJed, who proposed to his girlfriend in LittleBig Planet? Of course you don't. DimmuJed is not going to official wed his fiance inside of LittleBigPlanet, and is inviting people to join as "witnesses".
This is a really cool idea, and it also reminds me of someone who previously proposed using a videogame. TheRealPfhreak hacked an area of Chrono Trigger, and filled it with characters and dialogue that related to him and his girlfriend. It's actually a pretty long level, and the entire execution was very well thought out on his part. He even noted that his girlfriend was losing interest in the game, so he rushed to make it so she wouldn't be suspicious when he forced her to play it!