Hi – great question!
I can definitely see the utility of that. Right now though that’s something you would need to do by means of a customization (our Themer’s Guide outlines the basic steps) – though we’d certainly welcome this as a feature request if you’d like to post one 🙂
In theory – though arguably not the very most efficient way of doing things (but it might provide an outline you can use to kick things off) – you could override the month/loop-grid.php template. You could then test for “dead days” belonging to other months by inspecting the $daydata variable and, with a little arithmetic, figure out the actual date and populate the cell from there.
It’s a bit more involved than we can help you with but you might be able to take it further yourself and, of course, please do post a feature request!
Thanks!