Right, but you still didn't say why it would not work out. And I'm also pretty confident Marchisio can play a holding role despite him not being a real DM. He has the tactical and positioning sense to do so, in my view.
There is this perception around here that a DM must be placed into every single formation possible, which just isn't so, especially in a straight 4-4-2. As long as the two central midfielders can develop an understanding that accounts for one leading an attack forward, then having a DM that stays back all the time is not necessary. The system is set up so that both central midfielders have to do their fair share of defending and going forward, so it's best that they can do both. Our DM's, sadly, cannot, yet you sometimes see Sissoko screwing around near the opposition's box.
So I don't see any reason why we should not give it a try.