My tandem is a 26" wheel hybrid type using a 3x7 gearing set up. I've removed the flat bars and installed drop bars with Shimano 3x7 STI shifters, they're got a thumb button for shifting like Campag, but I can't get enough pull on the left shifter for the clamp-on STX FD to use all 3 chainrings, that's why I'm hoping the bar ends will work, and yes, they'll be in the end off the drops.
BTW, the STX FD worked fine with all 3 chainrings with it's original grip shifters. I realize I will have to lengthen the chain as well.
As I used to road race and still train with the boys, I usually ride a 53 or 52 on my single bikes, (I still love going very fast), so considering that the 26" wheel is smaller I thought a 54t would give my stoker and I a bit more speed for down hills etc.