First filter out all the tracks that contain one cover. For more than 2 you will have to manually do them.
Filter, Press F3:
"%_covers%" EQUAL "1"
Action:
Begin Action Group djatwork Cover Problem
Action #1
Actiontype 13: Export cover image to file
Formatstring for image filename: %album artist%- %album% %year% %publisher%
[_] Export duplicate cover images
Action #2
Actiontype 12: Import cover image from file
Formatstring for image filename: %album artist%- %album% %year% %publisher%.jpg
Import cover as: Cover Front
[X] Delete existing cover image
End Action Group djatwork Cover Problem (2 Actions)
Test on a couple of files first.
Also see this post I put up on creating a column for displaying cover art info:
/t/13562/1
EDIT:
On the plus side this will create a backup of all your Artwork to the co-existing folder if you have not already done so.