I honestly think tieing too many of the OT characters intot he prequels will just diminish the epic feel of the series and invite an unwelcomed "It's a small universe after all" effect.
However, if Solo were to feature I imagine his appearance would be facilitated by the Hutts in some way. Perhaps Solo could make a tiny appearance with his father in a Hutt palace?
But then, we know Boba Fett is being intruduced with his father, Jago, so maybe that option is out.
Personally, I would not see Lucas shoehorn every character into prequels.
Well, Jango is not in any catagory except for EP2 charactors. (see my sig) 馃槈
As for Han.. lets just say that the yellow hot rod Ani 'borrows' has "Special Modifications" to it. I wouldnt put it past them to have the owner of that car to just have one line. "Hey!" As the speeder takes off, but that may well be our Han.
Of course it may never be verified, but that is the extent of his screen time IMO.