Co-surgery, with PA assist for only one of the co-surgeons

Surgeon A and Surgeon B work together on a co-surgery and bill one CPT® code, each with a -62 modifier for their services.
Surgeon B has an assistant (PA) for just his portion of the co-surgery.

How do you modify the PA Assistant billing to reflect that they assisted only on the Surgeon B's part of the whole surgery, given that it's all one CPT® code for the entire operation?

Modifier AS seems to imply that the assistant participated in the entire surgery, not just surgeon B's part.

re: Co-surgery, with PA assist for only one of the co-surgeons

There should be no need for modification because the PA assisted on one procedure I would just put the AS modifier