Using DataGrid, how to handle arrow keys in cells

Okay, I know the up and down arrow keys work fine in a WPF DataGrid, unless you are actively editing a cell. Then the arrow keys won't move between rows, and I want them to work that way.

So how do I trap the arrow keys while I'm editing a cell? I mean, the up and down keys do pass through the PreviewKeyUp and KeyUp events, but how can I tell if it came from a cell currently being edited or not? If it is, I want to manually perform moving one row up or down. If a cell is NOT being edited, then I don't want to do anything.

Any ideas, here?