Greg,

Completely raising your boards will make tacking very difficult.

The standard Nacra rudder system allows you to set them at a shallow draft but, as Qb2 said, it puts a lot of stress on the hardware and the skipper.
You could break a casting $$$$

The previous owner of one of my old boats, a Nacra 5.2, had made a set of shoal draft rudders.
They drew 10"-12", were very wide and had alot of undercut.
He made them out of plywood with an epoxy coating.
I never used them so I don't know how well they worked.

When you say, "a la Hobie Cat", I assume you are refering to he 14 & 16 because the Hobie 17, 18, 20, 21, Fx/one, Tiger and Fox all have boards.
The 14 and 16 have asynetrical hulls with alot of rocker(banana boat).
The flat side of the hull gives the leeway and the rocker helps in tacking.