I see a great potential way to bring her back in season 5 if the season 4 finale plays out the way i think it does based on a few sneak peak videos that came out:
VIDEO: Three Chuck Season Finale Sneak Peeks (SPOILERS!) | ChuckTV.net : The fansite for the NBC series, Chuck
And yeah, ive wanted to see Jill back for awhile.
Also.. they really blew the whole Hannah storyline.
I think the Hannah storyline (and the last two seasons in general) would have been much better if the writers had any idea how many episodes each season was actually going to be. Mid-season in 3 and 4 there were quick wrapups of stuff that wouldn't have been needed if the network had just ordered a full season from the beginning. If NBC would just decide one way or the other, that would help.