Yes. Just attach the popup to a global field on that layout and base the portal on a relationship that matches from that field. (Use a global so users don't step on each other.)
The script steps you can use to force a refresh are Refresh Window and Refresh Object. Refresh Window updates all objects on the layout (and is hence slower); Refresh Object can be applied just to the portal (which will be faster, but may leave other objects on the layout in a pre-refresh state).
Thanks Mike. I've seen you replying to a number of queries on this forum and your expertise is invaluable - at least from my perspective.
The script steps you can use to force a refresh are Refresh Window and Refresh Object.
Though in this case a Refresh shouldn't be necessary, since the selection directly changes a relationship key.
And on that note: another technique (expecially pre-13) to refresh a portal (e.g. when filtering) is to set a/the match field of the relationship to itself.
Well, thank you. Don’t know about “invaluable”. So long as it helps.