Hello!
I understand your situation hopefully correct? You do not want to copy all IPTC data, only for the next one or two images, the CAPTION?
Then I know your problem. In IPTC editor there are buttons "copy", "Save and advance", "paste" and so on.
This does not help us because it ALL Data copying and pasting. Included fields that are occupied in Stationary Pad with variables and individually for each image.
So I suspect you have a similar function to insert it into three or four pictures only same caption, ex. "John Doe (1st left), Jane Doe (2nd left) ....", in the next pictures other peples names and so on?
Then I am with you and would find good, copy buttons for further switch, insert content only caption.
At the moment I have to do like writing Mick. Go back one picture, click in the Caption field and press CTRL + A, CTRL + C, turn in front again, paste in the Caption field.