Reasons it was not Kairi:
1) she wasn't there.
2) Sora's the first person to understand how useless she'd be in battle as shown in KH1; he was talking about taking on the Organization. Why would he mention Kairi?
3) Sora'd be damned to drag Kairi into the mess again now that she was finally safe on the restored DI.
4) You'd think he'd be more aware about a girl who's been a close friend for all his life, wouldn't you?
Either Roxas or Jiminy, though I wouldn't rule out a mixture of the two, like - Sora mentioned Roxas but everyone else wrote it off as him referring to Jiminy so it's still all good.
This happened right after CoM, and after Jiminy made his presence known by looking through his journal and finding the 'Thank Naminé' memo. It's not unthinkable Sora mentioned him, and on the contrary - Sora bringing it up as an after thought kind of hints further that it's Jiminy, seeing how the bug lives in the boy's hood and is always out of sight.
Sora, The King, Mickey, and "you guys" - it's the "you guys" that we can play with here, where opposed to Donald and Goofy that were visible, Jiminy was hidden.
Nam.