Thanks everyone for your replies! We just took the plunge a couple of hours ago - decided to go with an Electra Townie Balloon 8. (Apparently the last of those bikes available anywhere). They are building it up for us on Sunday! I am so excited to *hopefully* have it before the end of the long weekend.

Looks like there was enough seatpost left when both DH and I rode it to attach the stoker handlebars to the captain's (aha!) seatpost. The folks at this shop have installed that enough times, they thought it would be no problem.

I can't wait for my new bike! I'll post pics when it's done!