How do you integrate (html5) undoManager with execCommand to have a unified undo/redo stack?

Question

I have been working with html5 undoManager in firefox and have found it to work quite nicely, but have not found a way to get it to work with copy/paste and other non undoManager.transact items. In other words, document.undoManager.undo() and document.undoManager.redo() only undo and redo undoManager.transact items while document.execCommand("undo", false, null) and document.execCommand("redo", false, null) do a great job with copy, paste, etc. but do not undo and redo undoManager.transact items.

Thanks in advance.

Cheers, Alex