@Robmonster: Here you go:
http://blaut.biz/bookmarklets/myk.htm
Use the "
MYK:CFPR3" version of bookmarklet. You should also bookmark that webpage so you have place to check for future updates, once Amazon's changes/redesign brake the bookmarklet.
Clicking the bookmarklet adds "clearFPR!" (= Clear furthest page read) button next to book.