There are a number of standard ways to release a stuck parking brake: applying and and releasing the brake multiple times, lurching the car forward and back, bouncing the back corner of the car with the locked up wheel up and down, flexing the cable housing with your hand between the wheel and the spreader (where the main cable terminates and a shorter cable goes to each brake drum), rapping the backing plate with a hammer (but don't bend it) and tapping the front of the drum with a hammer and punch if your wheel allows you access.
But the time comes when none of these quick-and-dirty tricks work, and the only solution is to remove the drum and replace the brake cable and the return spring, which needs to be strong enough to pull back the brake shoes when the brake is released. The elegant (ie, proper) way to get the drum off is to back off the self adjuster screw through the access port in the backing plate behind the drum (over the axle and under the bleeder screw and hydraulic line). This almost never works for me when I need it, either the auto-adjuster is a little rusted or the force of the sticking emergency brake cable keeps it from wanting to turn. So my solution is to cheat, which risks damaging the seals on the wheel cylinder, but when I'm stuck, I'm willing to risk it.
