The README for the hack include an alternate method, which is that PM previous pop up as a tool-tip (when you hover over the PM title.) This is a happy compromise and my users LOVE it. Very clean, very nice. Makes it super easy to manage lots of PM's.
The hack's thread also includes a tip on how to make it user-optional:
https://vborg.vbsupport.ru/showpost....1&postcount=30