@BugDevil: Shion is Shion in the anime and in most places I've seen. Liko is Liko becuase someone whined the last time I called her Riko. I'm not going to get into the L vs R debate with you.
For me a proper doujin is one that is well-made, has decent art that resembles the characters reasonably well, treats whatever its pairing is with respect, and doesn't include any males. It is entirely possible to have proper doujins of crack ships. Speaking of which, aside from the Yuko x Everyone suggestion I made, I consider all of those pairings to be ships that have at least some foundation within the series. Mikan and Yuko have already gone on things that could be viewed as dates with each other, there have been plenty of indications that Mikan could have a crush on Momo, and the Momo/Lillith dynamic is just ripe for all sorts of stuff.