They use mineral oil, so you could use the yet-to-be-released tiagra 10spd shifters with it? No idea if the master cylinder is big enough, and I can't imagine 10spd on a touring tandem is going to last well either.
Maybe get some Kelly Take-Offs? That's as close as you'll get I think.
Yeah. Magura hs11 rim brakes paired with hs66 Road levers. Would love it if there is a compatible set of sti levers that would operate the same brakes