I've been thinking more about how to laminate the channels.
From thing I've read on the web one approach production houses take it to have top and bottom molds that simultanously apply pressure to the contoured surfaces of the boards with the laminate in place. In one case I read that up to 90 tonnes of pressure is applied an 20 minutes later the board is ready to drill and clean up.
Obviously not an option for home but the dual mold idea might have a poor second cousin that could be DIY'd.
The idea would be to use two rocker tables (or if you've got an adjustable table two different settings) so that you could first lay up the underside with the board upside down on the 'top' rocker table and vac bag it so the channels get laminated properly, then laminate the top side with the board vacuumed onto the bottom rocker table. You could use this second step to put a smooth finish on the bottom at the same time as laying up the top.
My non-adjustable 'brokite style' rocker table already has the jigs cut for the top rocker table as they just the excess material from cutting lower jigs. All that would be needed would be to screw the rocker surface center jig for the top rocker table.
If the board has very little profiling then it might be possible to do this in a one step process. If the top of the board is profiled then without support under the profiled pieces they would be bent out of shape e.g the rails might end up being bent upwards (which might actually not be a bad thing). I wonder if it would be possible to to cut inserts to support the profiled sections that don't leave to creases in the laminate? Maybe there is a way to use a hot wire cutter to profile the foam core? This seems like it would be a fairly high level of precision which might now be possible to do in the backyard.
Another idea, would be to do the profiling on the underside of the board. This would mean tapering the tips on the underside rather than the topside. This might work. You would just need to take this into account when calculating the rocker and concave and would need to make sure that the tapering was smooth rather than the typical well defined wedge that comes about using a router. The manual CNC ideas that Jorge Gonzales put me on to on www.skibuilder.com would work perfectly here. ( BTW check out Jorge's pro-setup http://cenitkiteboards.blogspot.com/ . Awesome!). This way the board could be layed up upside down and you could end up with the really slick finish on the top that you get on the underside when you use perspex or the like on an bottom rocker table.
The more I think about it the more I think this way could work well.
You could also use the channels to help control the flex by either carving them into the core for more flex or adding extra material to build up the channels for less flex.... This might just work.......