AP invoice payment date

We have this requirement to base the invoice date based on ship date of items from supplier rather than receipt date.

This is happening for foreign suppliers for which there transit time more than 1 month. For example the items are shipped on 24-Apr-2017 but received at client site on 26-May-2017. Now when the items are received and receipt is created after which AP invoice gets created , it has same date as of 26-may-2017. Hence the payment terms like CREDIT 30 make the payment during for next 30 days.

But as per supplier the items were shipped one month before and they are getting late payment. Hence we want to the invoice date should be considered on the bases of ship date.