The team shaped definately changes when Boateng is on.
Parker and Sidwell both seem to carry the defensive and attacking responsibilities, with Sidwell slightly more advanced but Scott having some licence to go forward. Jol seems to think Boateng should only have defensive duties, he mentioned him in comparison to Parker and implied Boateng wasn't a passer although he was a 'warrior'. He just sits deep which allows the other midfielder some freedom.
Parker, when fit, is the obvious first choice next to Boateng, although he's not really an intricate passing midfielder- he's all guts and his best position is the one Boateng fills.
We don't really have anyone to play that central role, Parker and Boateng would have drive and could create chances (Parker the more advanced). With Parker out I think Boateng has to start and my choice would be Karagounis playing just in front of him.
Technically, he is the best of our genuine CM options. Maybe Kasami could be the answer in central midfield but even with Boateng or Parker sitting behind him I think he would still be too indisciplined to hold position and at this point in his career we're better to encourage his attacking instincts and play him more forward.
Sidwell as a starter does not inspire any confidence- he is competent in a number of areas but doesn't really excel in any.