I think this is faster than Mini-Map casting and far more accurate. With practice it is super fast.
Check out the video demonstration here.
Basic Guide \ Idea
1. Put all queens on 1 hotkey.
2. Select queens.
3. Press Spawn Larvae hotkey.
4. Press Backspace once to center on a hatch.
5. Hold Right Side Shift. (With left hand thumb, do not release at all)
6. Click Left Mouse Button + Backspace (Hit backspace with left hand index\middle finger) <- Repeat this series of actions rapidly. Hitting LMB and Backspace over and over in succession.
7. All hatches are injected.
I numbered the hatcheries 1 through 6 in the video with supply depots, this helps show how fast you hop around and inject larvae.
Hopefully this is a technique other are using, or can find useful.