An orphaned query with no response; can't have that!
Though this thread is over a year old, a friend asked me the same just the other day; mounting his handlebar bag (an Ortlieb Ultimate 5 medium) on a Thorn 105mm Accessory T-bar did the trick for him. It took a bit of fiddling, but by placing the T-bar above the first spacer atop the upper headset cup, the top lid of the HB bag was able to sit below the cable-exit for his Sora levers. He rides a fairly large frame (another brand) with his Sora "brifters" mounted fairly high on the 'bars, so this might not be possible on a small frame with more limited vertical clearance. He also prefers his HB bag to ride dead level, and this aids clearance as well. He does have to bother just a bit with the lid to clear the loop of cable housing, but it isn't much hassle and allows for a HB bag, so he's happy.
This solution beat the other one we were pondering, which involved using a spare set of v-brake "noodles" to re-route the Sora cable where they left the lever. We didn't pursue the matter, but concluded extra friction there might well add friction and affect the indexing. I have seen it done by others, however.
Best,
Dan.
