I haven't seen schematic 2/2 yet, but here's a couple of thoughts (I kind of wonder about the strength of a whole mess of little wood pieces -- plus it would be a glassing nightmare):

How about creating the C-shape that makes up the 'U' of the recess by taking, say, a [1 1/2] X [1 1/2] X [something long] piece of hardwood and hollowing it out on a table saw. Then by cutting off sections at varying angles and gluing them around the opening (similar to Nick's method,) then glue on small pieces for the acutal coaming lip. Alternating colors would look cool with this method as well.

Similarily, the C-shape could be the backwards 'C' of your diagram, the one that makes up the lip, inner vertical wall, and lower surface. This could be glued to the outer ring of vertical sections.

Dean