The two levers and one brake can be found on some time trial and triathlon bikes. You have a lever on the base bar, as normal, and then a 2nd lever that can either be another TT style lever, or a gear lever that pulls brake cable, mounted to the end of an aero extension.
It isn't common but gives the rider some braking from the aero bars without going out of an aero position, on to the base bar.
The system can be reversed so 1 lever operates two brakes and this is normal for tandems and disabled cyclists.
I am still developing an idea and may not go ahead with it so how about you take this from Raidan , and i will get back to you. Don't hold back on using it ,if you need to , as the other options i mentioned are current, and not things from long ago , so i will be sorted.