Pardon me if I state the obvious, but you didn't say which position on your levers you are using--the V brake position will pull the most cable, of course, even on canti's. Also, you may be able to figure a way to incorporate one of those eccentric wheel adaptors (V-daptors) into your cable routing somewhere. These two options may be a bit much for the front brake, though, with its short cable length.
CC