Jeff,

The Subaru hillholder was predated decades by the Studebaker version. There is a product called a "line lock" which was sold by the likes of Hurst and/or Mr. Gasket. This gadget locked the front brakes so that drag racers can do burn-outs with the rear wheels while keeping the vehicle on the line just before launch. I'm sure that can be adapted for use as a hillholder. Most VW buggy places also ssell a product called "park lock" which is plumbed to a hydraulic line to do basically the same thing. Press a button and go. I have a couple of these lying around. They are a fairly common item. Most are sold via street rod magazines by rear disc brake companies. They are used as an inexpensive parking brake alternative by many (useless as a emergency brake in that application).

BenT