Two E-brakes would probably be the simplest to build, but I imagine it'd be a PITA to use. Specifically, I'd expect the ratchet mechanism to leave you dragging a wheel when something else (steering, shifting, operating something else) distracts you. You could disable the ratchet mechanism, but then they're no good as parking brakes. Add some kind of on/off for the ratchet... but then you're still banging your knuckles against one handle or the other, and you have to release one and grab the other to change sides. Seems a little cumbersome.
My stupid idea is to take the stock e-brake, bolt it to a separate plate, and hook that plate to the floor with a pivot. Leave the stock cable alone. Then, you'd hook new cables to the sides of it, route them underneath the car, and hook one into each leg of the factory system. So, you're driving, and say your right rear wheel looses grip. You grab the e-brake, and shove it to the right. It pulls the cable, the wheel slows, ta da. Need to do something else? Let go, it'll pop back to the center. (If it doesn't, add a spring or two.) And, since the stock cables and ratchet mechanism are still there, you can still use it like a regular brake.
Here's a crude line drawing. (New cable is in blue.) The arrangement on the left makes more sense (no stupid pulleys), though it may prove more difficult given the width of the console.
(It says 'spliced to stock,' but the pen was dying.)
This seems more user-friendly to me. Of course, you'd have to butcher your console a bit, but it's not like you wouldn't have to with two handles.