Originally Posted by
AeroGut
+1 on this, especially given how big your frame is. You've got a lot of room between bars and front wheel to work with, so it would be easy to rest the bag on a rack there and not have to worry about supporting it securely and maintaining rigid structure while it's hanging on the front of the bars. If you can improvise a decaleur type mount, that would make it really secure on the rack, but it's not necessary.
I probably didn't really sell the approach, so I'll comment a bit more to say I really liked it and found it superior to a handlebar mount for those cases where it is an option. I even went so far as to mount one on a bike that didn't have canti bosses using p-clamps, but that is kind of a kludge. It worked but wasn't as nice as the canti boss setup.
There are other little racks that would work. Some of them are crazy expensive though. I bought several of the sun lites at $12 a piece and them pretty adequate. I even used them as a rear rack and loaded them more heavily than they were intended to be with no failures. One on the front and one on the back works great for my old rigid MTB for UL on/off road touring. My newer MTB doesn't have canti bosses or I happily use them on it.
I cringe when I see something a similar size for $85 even though it is undoubtedly higher quality.
BTW, I have also just strapped a little camera bag to the stem and let it hang in front of a bikepacking style bar roll. It just sort of hung in front of the bar roll by it's straps. It stayed fine and was quick to grab and take with me. Not sure if it would work as well with a bigger bag, but it probably would. I guess it would depend on frame size, bar height, and size of the bar roll. If you were nervous you could add a bungee, but I didn't bother.