Reverse / Cancel POP invoice

Scenario is that you have entered a stock POP invoice incorrectly, for example the qty invoiced is too high. It would be useful to reverse this invoice so that you can re-enter correctly. The current process involves having to create a new PO, entering a return /credit and writing off the original PO, sometimes this isn't really suitable as the original PO may have many other lines on it that are part / fully processed.