LuluXCC is the most likely pairing to happen if he pairs with anybody, be it a real relationship or one-time pity sex. He's closer to her than any other person in the show period, let alone Shirley or Kallen. Whether or not their relationship will actually go that way is just dependent on whether or not they want the show's plot to allow it, but I highly doubt we're going to see him hook up with anybody else. >>As for Kallen, Lelouch flirts and teases her a fair bit and wants to fuck her so atleast Kallen makes Lelouch act not gay.
I'm pretty sure the flirting and teasing in season 1 was just him being a dick to her to throw her off the trail (she'd be less likely to suspect someone she didn't like to be Zero.) And as much as I might sound like a delusional shipper or anti-shipper by saying this (and I don't 'ship' any pairing here, I'm just analyzing) the scene in episode 7 was *clearly* just because Kallen was female, hot, and there, not because he actually feels that way for her.