I may be mistaken but I don't think there is any way. Single Player files are saved to your computer hard drive and realm character files are stored on Bnet's. Unless you know someone that works at Bnet who can copy and send them to you, you're out of luck. However, if I AM wrong, I would like to get a copy of the files for my realm characters also.
You are right Taurgon, you cannot transfer to single player from realm. There are probably programs out there that let you edit single player characters but I don't know of any. There used to be one for 1.09.
I'm pretty sure there is a program to do it, because character information is stored on you hard drive (although it is not used on the realms). I also can't say what that information contains, just that it exists.