[Disclaimer: as a GG trail ambassador I got this pack for free. The modification itself is neither supervised, condoned, or monitored by Gossamer Gear. Use at your own risk.]
I couldn't help myself. When I have what seems like a good idea, I have to see if it works. In this case, if you ever intend to use your Gossamer Gear Gorilla to haul a ~27 pound mountain bike and 4 days of gear over a 10,000' ridge, you might consider the following.
Photo by Casey Greene.
Kifaru and other packmakers who specialize in obscene loads have stays which insert from the bottom up, and pockets built into the hipbelt which help retain the stays when the lumbar pad folds over and attaches. You can do something similar with a Gorilla by sewing pockets into the belt and cutting holes in the backpanel so the stays can protrude out of their channel and into the new belt pockets.
I laminated (with seam grip) ovals of 500D cordura to the backpanel fabric about 7 inches above the bottom of the stay channels. This layer is intended to keep the thinner backpanel fabric from ripping or unraveling. Then, very carefully, cut a hole in the Cordura, backpanel fabric, and the layer of grosgrain which forms the back of the stay channel. Don't cut the outer layer of grosgrain, or outside the stitching which holds the stay channel in place. Melt the fabric layers into an ellipse. Squish the fabric edges together. Make the hole just big enough for the stay to go through.
The stay pockets in the belt should be pretty burly. I used a double layer of ballistics nylon, which holds stitching well and is resistant to abrasion. Pockets were 9" apart center to center, which matches the spacing of the stay pockets at the bottom of the pack.
Bartacks at the corners, and triple stitching down the edges. Bartacks along the edges wouldn't be a bad idea, if your machine can do it.
Once completed, the stay can be used as stock, or pushed out the hole and inserted into the belt pockets. Weight transfer with the later is quite a bit better. The only limitation is that the stock sitlight pad might not be enough to alleviate pressure points from the stays in the belt. A thin, stiff layer of foam under the sitlight would probably solve that. I haven't got there yet.
As I said, use at your own risk.