The only other option would be to select the images that all need the same caption, open the Metadata (IPTC) Template ( Command-I or Control-I shortcuts ), click the Clear button at the bottom, enter the new caption and then click the Apply Template to Selected button, ( Command-Option-A or Control-Alt-A shortcuts ). I'm suspecting it will be faster to copy and paste one caption to the next, for 4 or less images. If there 5 or more images that need to same caption, Applying the Metadata (IPTC) Template should be faster.
Best regards,
--Bob