Haven't tried it on any other widows but I did try modifying the action window. Added 2 inventory boxes to the bottom. The right is global to all tabs and the left is specific to the tab.
If you want something to show up on all pages just put it after all the page commands and it's Peices to the screen items instead of the pages section.
You can see my action box at
www.cohort.cc/~taraddar/TaraddarUI.jpg
and download the files at
www.cohort.cc/~taraddar/TaraddarUI.zip