I don't carry anymore because of the rules/laws on college campuses in Texas, but when I did on a bike I always preferred the tank bag method. You can get away with a lot in the way of securing it within the bag, it's always pointing away from you and it's accessible at all times. I typically carried a tail bag as well. If I needed to carry things in, holster your sidearm and pack the tank bad with the items from the tail bag and carry it away.
My .02
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Oh and in my opinion(I'm generally a LnC kinda guy as I carry 1911's) I only carry in this situation with the chamber empty. Should anything go absolutely wrong, a wreck, whatever the weapons only in amber.