I have a master cylinder with a handle dedicated to a seperate caliper for an e-brake and you could adapt a locking pin to be a parking unit.
Saw this at the recent PRI show. Thought a few here might find it a useful solution. I have a car i might try it on.
Nobody should for a minute consider it an "emergency brake"..
My application is an IRS, I'm pondering fabbing a Ti mini solid disc on the rear DS yoke and mounting the brake there.
We'll see.
And I have no connection with Wilwood other then what i have shared here.