You can pass along custom info through the custom field in the checkouts. In the Direct Pay you would update this on the confirm page in the local checkout on this page. On step 4 of 5 find the custom field and bind whatever value you would like to it.
For the Express Checkout pages this is on the checkout page, and the server behaviors on the pp_confirm page. You just ensure that you bind the custom field with the value you would like to pass through.