I've not used one for a spare fuel container on this bike...yet however I have personally used these bottles on my other bikes and ATV's. One one of the ATV's I mounted a 'Tractor Manual Tube' (Google it to see what they look like) to the Quad which I carried the fuel bottle in. Worked pretty well and survived a couple of years of hard off-roading all over the Mojave and Utah before I sold that Quad and moved-on to another which I mounted a larger fuel container on.
Honestly though, most of the time if I feel the need to carry the MSR fuel bottle I just carry it in my backpack. I've yet to have one of these bottles leak and if I'm carrying gas I'm going to be far off-road so I'm not worried about an on-road collision. One thing I really like about the MSR Fuel Bottle is that if you ever need to transfer gas from one bike to another, it's pretty easy to get the mouth of the bottle under the tank to the fuel line.
These days most of the time if I feel the need to carry extra gas I use a Roto Pak fuel container. The one I use holds ~1.5 Gallons of gas, though they make many different sizes. I've attached mounts for one of these containers to two of my bikes and one of my 'Buggies. Having more gas then I need is nice and I frequently end-up sharing it with others.
The only drawbacks I've found with the Roto-Pak is that it's really hard (if not impossible) to get them shipped to California (no biggie, I generally go to Arizona, Nevada or Utah once or twice a year and they are readily available there). That and once you start carrying one, most of your friends will expect you to carry it all the time.