Myself, I rarely use my e-brake. My rear brakes are so out of adustment (and quickly fall out of adjustment in 2 weeks), that I haven't had a working e-brake in a while. I don't miss it much.
But a roadside inspection would call upon one without a doubt. I read an article about using an ABS valve to manually isolate your brakes--just like a brake line-lock on dragsters.
It wouldn't do much in a real emergency, and would require a small amount of power to keep the brakes locked, but I'm hoping it would satisfy the inspectors if you had to demonstrate a working "e-brake".