I bought my CoMotion Primera 4 years ago, I think it was. At that time, for $500 extra, you could get "custom" frame geometry. If you're interested, check the CoMotion site, contact them if necessary to see what would be workable for you and what the options are.
As pointed out above, some of these bikes are available in L/L, M/M, S/S and L/S and that last is what you're looking for- but it does exist.
By the way, I'm a little over 6' and the CoMotion "Large" fits me.
Also, the Primera is a semi-compact frame, meaning the top tubes are a little lower on the frame, which lets it fit a wider variety of sizes.


For reasons unrelated to bike size, what works for us is for the stoker to clip in with both feet and stay clipped in until we stop (as opposed to both of us pushing off with one leg unclipped, which is the more common way). Anyway, with that technique, the stoker doesn't necessarily have to have ANY standover clearance- so you have more flexibility in fitting a stoker on a tandem than you do fitting her on a single bike. Or to put another way, the stoker may not be able to even straddle the top tube but still be able to ride the bike okay.


If possible, rent a tandem and test ride first. When the riders are mismatched in size, you can get the proper bike to make that work okay. But when you do, your pedals are at the same height, which makes the stoker sitting much lower, which means she's staring at your butt instead of your shoulders or head. Which is okay, too, assuming it doesn't bother her.