[Bill Baer]

Pro 318

Here's a link to a diagram to plumb a staging hand brake which is common in pro stock for staging but could also provide braking if the linkage in the foot operated master cylinder failed
http://secure.chassisshop.com/partlist/5465/
But as you say it may not be legal also a second master cylinder plumbed this way won't help if you have a line or caliper failure. For that you would need a complete separate system
Check with CNC they could provide you with better info than I.