Sign Lannan, sign Pelfrey and let 'em duke it out with whoever's left after any trades. Loser(s) gets sent to the bullpen, traded, or slotted in the rotation by midseason.
Should be able to piece together a good rotation and some long relief out of Santana, Lannan, Harvey, Pelfrey, Niese, Familia, Mejia, Wheeler and Gee (assuming Dickey is traded). Pick the best of the bunch, turn 'em loose and re-evaluate at midseason. Aside from Wheeler and Harvey, any out of that crew could become additional trade bait at the deadline. On the other hand, if they flop or get injured, you have some insurance waiting in the wings.