"Does a bear sh't in the woods?"
not-Jack is already subtly positioning himself to be less obvious, in anticipation of disappearing completely into the crowd the moment Bernie is far enough away. He's thinking: if he disappears, Bernie will probably run straight into Jack and think he's not-Jack, because that's how Stories work, and Jack is a creature of Stories ... at least, that's how not-Jack imagines it going. And that's Bad, obviously. But it's also kinda Good, maybe. It's good because not-Jack can just shadow Bernie and find Jack when Bernie inevitably runs into him.
So that's what not-Jack intends.
Shadowing someone is Wits+Stealth. Modifiers?