Yellow border around all sandboxed windows?

[slbox]

I have "Display a border around the window" checked and "Display the border only when the mouse is in the window title" unchecked. That puts a yellow border only around the active window. Is it possible to add a feature to make it put the yellow border around all sandboxed windows that are visible on the screen? (I would have put this in the feature request forum, but I don't have permission there.)