I find that the best use of a handlebar bag is being able to reach into it while I am rolling, whether it be for a bit of food or my point and shoot camera that I can easily operate with one hand or a bandana to wipe my nose or something like that. In other words, if it requires two hands, it is not in my handlebar bag. I can't hold the DSLR while operating the zoom with only one hand and I might not be able to get the lens cap off with one hand.
Thus, if I had my DSLR on tour, I would have both feet on the ground when I used it. Have you considered using a rack top bag for your camera gear? I have not put a rack top bag on my front rack before but if I was going to carry a DSLR, I would consider trying that to carry the camera and lenses.