I had QL issues for nearly a year. If you're suffering an acute attack, putting it under a gentle stretch will stop the muscle from spasming. As BBB alluded, the QL seems to suffer most when the musculature of the trunk isn't doing it's job supporting the body.
The QL acts much like a guide-wire holding up a tent. If the tent-pole isn't doing its job (in this case, primarily the multifidus, but weak abs will also elicit hypertonicity in the spinal erectors), then the guide wires are overly relied upon to support the structure.
After reading Stuart McGill, I found that unilateral leg work took care of my issues in a matter of weeks. I don't mean single leg knee extentions, but farmer walks, dumbell lunges, etc. Basically anything that forces the trunk to stabilize itself while ambulating. McGill suggests even hiking on uneven terrain with a weighted vest will work. While suffering from an acute episode, I like doing light-weight deads to warm the area up. You can try single leg deads, but know that your QL is responsible for hiking your hip and if you catch yourself doing so, you need to pause and really focus on keeping length between your hip and lowest rib.
Edit: I think the key to getting the QL to release is to stretch it while keeping a neutral spine. I know that seems strange, but one of the best things I've found is to traction my body from the hips. I discovered this at an Iyengar yoga class. They have these rope harnesses you put around your waist, then invert. It put a really nice, gentle stretch on my QLs without doing a side bend or a twist which just seemed to irritate an already cranky muscle. I tried an inversion table, but traction from my feet wasn't specific enough to my hips to be of benefit.