Actually, Alan, you can balance a pair of mechanical brakes with a single lever. They make those too. It uses a toggle to equal the load on both sides.
Go check out the great selection over at Coventry Cycleworks. They would be happy to have you sit on one or two... and maybe even send you out on a test drive.
And they also make differentials for Delta's. I'm sure Coventry has a few of those to look at too.