Folding Surfboard Rack

Background: 

The beach is 0.8 miles from my apartment.

 0.8 miles is a perfect distance if I want to walk to the beach and lay in the sand or snorkel or bodyboard, but I want to surf.  0.8 miles is too far to haul a surfboard on foot, but it would be a shame to use the car when the beach is so close.  The solution is to find a way to carry my surfboard on my bike.

I am not the first person to consider using a bike to transport a surfboard.  In fact, A LOT of people have already solved this problem with all sorts of different bicycle mounted racks and trailers, but none of these racks can be concealed when not in use.

Concept:

I am working on some initial sketches for a seatpost mounted, surfboard holder that folds into a standard seatpost rack when not in use.