If your going for a Nick Drake guitar sound, big and fat and rich is the wrong direction. I can't remember where I read this, but according to John Wood, the man that engineered all of Drakes sessions, on recordings Nick Drake used a Guild M20 - an all mahognany 14fret, 0 size body - which might explain the pluckiness I hear on his recordings (maybe that's compression...dunno, I'm a guitar player.)
I find the richness of Drakes recordings lie in his voice, melodies and playing style (weird tunings and fingers), not in his guitar 'sound'. In fact I think the lack of richness of his guitar tone amplifies the haunting qualities of his voice. I think you'll be hard pressed to get to that sound with a Martin Dreadnaught, or even a Martin small body. All of my Martins, big and small, have a....um....richness to their tone I've never experienced from a Guild of any description, though I love the old Guild small bodied varieties for thier unique sounds.
Maybe a single mic on the dreadnaught up the neck might be a way to go or some of the other techniques suggested in combination with the player concentrating his pick or finger attack near the bridge for a tighter more focused string sound, staying away from the open woodiness found when playing near the neck.
Best of luck!