My Counterpoint Opus II (semi-recumbent tandem) is from 1984, before the dawn of V-brakes. The front wheel is directly below the stoker's seat, so there's no room for a cable hanger; the cantilever was modified into a V-brake exactly the way OP means, and I'm pretty much 100% certain the bike was designed to have this brake configured this way; there's really no other way the brake could have been hooked up. It's very effective. But I don't remember the details.