Originally Posted by Retro Grouch
I don't think that you'll have any trouble at all. Many tandem manufacturers produced flat bar bikes with road front derailleurs for years before Shimano saw fit to produce a shifter specifit to that purpose. I've probably worked on dozens of bikes which had that particular combination.
So you'd recommend going with the flat-bar shifters and the FD-6500? Certainly seems worth the risk.
Btw, what about cables? I see cable "sets" for these groups. Do they contain necessary parts or should I try to adapt what's already on the bike?