How to make taskbar button menus wider

I'm running Vista x64 with dozens of windows open at a time. My taskbar is set with "Group similar taskbar buttons" enabled so when I click on a grouped item in the taskbar, I get a "menu" that shows the titles for the individual windows that were grouped.

Question: how do I tell Vista to allow that menu to be *wider* so windows with really long titles don't have the text cut off?

Unfortunately, there is no easy fix for this. When you have many windows open you're going ot have to put them somewhere...

Cheers