Yep, you run the line going to the rear brakes though the staging brake and then from the staging brake back to the rear brakes. this keeps the brakes functional on the foot pedal and with the staging brake.
BTW, ive never had an issue holding my car still with just a properly adjusted and working stock ebrake. The only advantage I could personally see from a staging brake is that it automatically releases the brakes just by simply letting go of the handle vs having to actually put the brake down with the ebrake although you can modify the ebrake like the drifters do to do the same thing by removing the lock on the handle. Ive just never seen the need to spend the money on doing a staging brake.