Move the camera across the line during the shot (dolly, Steadicam). The audience watches the geography change.
Cut to a neutral shot on the line (head-on or from behind), then cut to the other side.
A new action resets the line: a character moves, someone new enters, or the eyeline shifts to a new person.
A teaching model. Super 35 sensor (24.9 mm wide), 16:9 frame, level camera at 1.2 m (seated eye height) or 1.5 m on the street. The line runs through the two characters' eyelines; in screen-direction mode it is the walker's path. A camera within 20 cm of the line counts as a neutral, on-the-line shot.