Not an expert, but it sounds to me like you have a wrong diagnosis... On every vehicle I'm familiar with, the e-brake cable runs from the control (pedal, lever, whatever) in the driver space back towards the rear wheels, where it will connect to a "bridge" or cable splitter that converts the single cable from the control to a dual cable that goes to each rear wheel. The brake engages when the control causes the cable to tighten, and disengages when the cable loosens. The cable SHOULD be somewhat slack when the contol is released, usually there will be a spring to help disengage the control, and springs in the rear brake mechanisms to pull some slack in the cable and allow the e-brake to disengage.
If the cable is slack at the bridge, but the brakes feel like they are still engaged, either the cables to the wheels are corroded and need lubrication / replacement (very common in vehicles in salted roads areas, especially if the E-brake is seldom used) or there is something wrong with the brake release mechanism inside the wheels. Possibly the issue is that the mechanic got the brakes overly tight as EBL suggested - most brakes these days are automatically adjusting, and shouldn't need any mechanic adjustments unless possibly right after a brake job.
A stretched cable should keep the brakes from engaging, not causing a release problem.
If I was a betting person, I'd put my money on one or both of the wheel cables being sticky, and not releasing properly - this would cause the brakes to drag, and keep the slack in the cables from getting used up by the release mechanisms, with the excess slack causing the sloppy feel at the pedal...
Gooserider