Someone mentioned this in another thread and it is a great tip:

https://www.yotatech.com/forums/f16/adjusting-rear-drum-brakes-easy-way-43741/

I got decent results but needed to accelerate in reverse to 10 mph before yanking the parking brake over and over. Accelerating to 5 mph didn't make any difference. Now the parking brake goes up 5 clicks and there is an increase in response to pedal pressure - indicating that the rear drums are now helping out the front rotors. This translates to longer front rotor and brake pad life. Don't know if we can say the same for the rear drum life.