Oh, totally forgot about that...um, shift cables are universal but brake levers are not. The head that hooks inside the levers are different. Some come with cables and housing, some do not. You could go to a bike shop and ask for road brake cables:

http://www.bikeforums.net/showthread...531&highlight=

The right one is road and the left is mtb.

You can use the same housing, but if it is old, you might as well get new.

The cable will cost less than $5. Like BCRider said earlier, you would need new housing for at least one cable not matter what due to length, however, I can't imagine how I would cleanly route the housing. Usually brake housing runs under the bar tape, but with your add-on drops, that 90 degree angel is too extreme

I suppose you could just let it hang out but because they come out where the lever clamps onto the bar they would be awfully close the to bar itself and might be annoying.