A friend was in town a few weeks ago and showed me this technique. It’s not a Koei-Kan technique so I can post it here. Which is good, because I want an easy way to ask people about it – I can’t tell what I missed.
You deflect the punch while shrimping out of guard. The punch gets directed into the ground, while you flip your leg over the attackers head and go for the arm bar.
Full disclosure – I am posting this technique since I think I missed some of the subtle parts of it, and this makes for an easy way to ask.