[Dustin]

I don't think existing rules cover this - GURPS rules all seem to assume that the archer is performing a full draw, maximum power shot. The highly skilled fellow in this video is (in my opinion) mostly trading power for speed, using partial draws and an intriguing, but awkward arrow-readying technique that I think would compromise his hand's ability to pull a 100-lb+ warbow.

Together, I might stat it as a Technique that reduces the penalty for Rapid Strike but penalizes effective ST while doing so.