I'm pretty sure Petzl discourages using Gri Gris as rope soloing devices as they are not intended for that purpose, but folks do it fairly frequently. From Andy Kirkpatrick's website: http://www.andy-kirkpatrick.com/article ... 101_part_1
"Although it’s not meant for rope soloing, the Petzl Grigri is by far the most popular rope soloing device, probably due as much to its low price as well as peoples experience with it, rather then its safety record. Some climbers modify their grigri to allow the rope to feed more smoothly, or attach a loop of cord or wire so they can fix it to a chest harness, but both involve drilling or filing, both of which compound the feeling that you’re doing something wrong. Beyond the fact that most climbers are comfortable using a grigri, its main drawback is the fact that it’s very easy for the handle to become tangled or snagged, and so stop the unit from locking off. I’ve used the grigri a few times and have taken two falls, one that it caught, the other that it didn’t (I was saved by an aider clipping into a piece of gear on the way down!). Another problem is the device can only be attached by one karabiner and unlike a knot, has a good chance of loading the karabiner badly (a brit soloist took a monster lob off el Cap a few years ago when his DMM Belay Master attached to his grigri snapped - being saved by his back up knot) . When using a grigri I would use a steel mailon to attach it to my harness, and make sure to always have a back up knot, as well as reduce any clutter that could fowl the handle."
There is a modification that folks make to the Gri Gri for use as a rope soloing device. Here are instructions on how to do it: http://ulrichprinz.de/alpin/equipment/selfmade/