Firstly, forget Aquilani. That's not even on the table. He'll never wear a Reds shirt again.
I think Spearing is the closest ready-made replacement we have for Lucas. He did fantastically well at the end of last season when he got a run of games in the team, so he should be given the chance again to show he's pushed on even more, imo.
I think it depends on the game though. We won't always need to play that system, so in some games i'd like to see a pairing of Adam & Hendo, or Adam & Gerrard when he's back.
Alternatively, there's the option of playing Spearing in front of the back 2, with Adam & Hendo in front of him, 2 wing forwards and 1 centre forward. We've already played this system this season, and it's one I think we'll see used a lot in Lucas's absence.