McGrath, I don't want to be mean, not very anyway, but have you checked a good music store for the Keyser "Drop-D" capo? They've been out for a couple of years anyway. They have a cutout where they would contact the low E, to get the same effect.

One of those on third fret, a standard one on first fret, use D positions. Best way to play in F. Use G positions, best way to play in Bb.

Peter.