I took a somewhat modest approach to building our Calfee Tetra (2007 frame). With BB7 it came in at roughly 29lbs before adding bottles, pump and req'd support tools.
Since building the tandem I have personally reduced the combined tandem/team weight by 8lbs and plan to reduce it by another 8lbs over the next 2 months - all at no additional $ cost. That is a 16lb reduction without the need to alter the original build.
If you subtract my reductions from the original tandem build weight, at 13lbs we will be riding a UCI illegal weight bike
---
PS: If you really want to save grams, limit your stoker to jersey pocket capcity only and do not provide extra storage space in the form of bags. I know, that just ain't being stoker friendly...