There are return springs on the rear calipers, but the slack in the cable itself needs to be removed by adjusting the adjuster under the drivers door area. If you look at it from under, you'll see the metal bracket on the rear part of the cable, and the threaded part of the front cable. You just get a wrench on the nut and tighten or loosen it to adjust the tension in the cable. It'll probably be siezed, so you'll want to soak it with WD40 or something similar first, and don't be surprised if you may have to heat it up too.
Just make sure that your rear caliper are releasing fully first - use a pry bar to pry the e-brake levers back and make sure they're fully disengaged, cuz if they're binding at all, they won't release completely, which will leave slack in the cable, allowing it to hang down like that.
