If there is either a tandem or bicycle polo club in your area, check with them. My son's freestyle bike has a clip which combines the two under-the-downtube brake cables for attachment to the straddle cable yolk. (A freestyle bike has trick brake cable routing which permits the front wheel to be rotated continuously without binding the cables.)
For tandems, Mafac used to make a lever with two cable pulls.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069