Is there a way of recording sales without having a deal on Pipedrive?

80% of our business will be deals that we track through the sales process and we know are coming in advance.  Many times however, we have orders where customers have simply emailed in a purchase order.  What is the best way of recording this on pipedrive?

If we add a deal on pipedrive and win it immediately for the ad hoc orders, that then scews the deal velocity averages.  

However, if we don't put those orders on pipedrive at all, the revenue figures are incorrect.

Any ideas, gratefully received.