Have a script performed when the popover opens set a merge variable to a list of the data. Place the merge variable inside the popover.
Locate the popover just outside the portal. Use a regular button inside the portal row to set a match field used to update a relationship used for a portal inside the popover to show the desired records and then uses go to object to open the popover. You can make the popover button invisible and position it so that the popover appears to open out of the side of the popover.