If you fire your shot and jump immediately after, pressing your mouse (or key, whatever you use) to reload, it auto-reloads while in the air. Hard to get the timing down but definitely repeatable.
Also, as a question, was it intended to not be able to fire a crossbow while falling (by just walking off an edge), or is that a side effect of not being able to fire while jumping? Last chance suicide dives were awesome, sad to see them go.