Ok, that is most certainly scriptable. I will offer a script if nobody else does, but my script will either be cumbersome (using offset of ā,ā and then redefining the text in each round) or I will need to read up about how to use delimiters in AppleScript. Whilst the latter would do me good, perhaps somebody who actually knows will beat me to it 
(edit: I think I can use @pete31 post here to put something together)