Tandem 2nd-seat Conversion Ideas

So, since I gave my kid my Specialized, I am down to a Schwinn tandem I purchased a long time ago.  I repainted it and had J&R Cycle & Ski rebuild it in 2010, and was thinking of trying to trade it for a tall-framed hybrid or comfort bike.

But now I am thinking about keeping it, and replacing the second seatpost with some sort of storage assembly/kick stand contraption.  This could be my daily driver with a little work.  I have a universal-gear-styled adapter with seat-post dimensions, I just need a good idea for the rig.  I was originally thinking about a 5-gallon cooler...

Your thoughts?