Clear Clipboard on cell selection

I am trying to stop users of a spread sheet copying and pasting into the worksheet from external sources which is stuffing up the formatting, Ihave tried Application.CutCopyMode = False on cell selection which works if the data was copied from somewhere on the workbook. When I copy from an external source it does not disable the paste function.

So what I need to do is clear the clipboard when a cell is selected on my worksheet no matter where it was copied from.

Any thoughts or assistance with this would be greatly appreciated.

Thanks JBeaucaire's I will give that a go.