Very nice bike.
I would recommend some Thomson seat clamps as they work much better than some lighter weight alternatives I tried. I found that the captain's seatpost needs to be clamped more firmly on a tandem than on my single bikes to avoid being turned round by the stoker. The thomson seat posts are somewhat prone to this from their machined surface finish.
Since you mentioned light weight, other weightweenie thoughts without spending $$$ on new cranks and wheels for instance might include:
i-link cable outers
extralite headset expander
masterpiece seat post, or at least the head parts as this is where most weight is saved
extralite stems
ergonova ltd bars
kcnc jockey weels
fibrelite carbon chainrings for the left side of the bike
stronglight chainrings for the right hand side
kmc xl10 chain throughout
SRAM powerdome or Dura Ace cassette (I would not go lighter than this personally)
swap rim tape for veloplugs
kcnc or similar lightweight skewers (I am dubious about this on for the rear wheel, but for the front should be fine)
supersonic tubes
schwalbe ultremo tyres
aluminium butterflies and ti axles for the speedplays
Once you've done all that, drilling out the waterbottles can be effective ;-)
I would discuss parts with rob, as he is definitely an expert in weight weenieism.