Multiple contacts and emails for customers

We are using Xero, Ship Station and Routific.  A lot of our customers require emails sent to specific email addresses (often an un monitored address) on the day of shipping, so this is the email we select as Default.  We have found having a default email means that those details get pulled across as the contact on the invoice.  We would like to have multiple contacts within each customer, eg. accounts, invoices, statements, warehouse. This would mean that when an invoice is created, the correct contact is auto loaded not just the default.   This is imperative as the information needs to be pushed through to ship station as well as Routific app.   Using the Ship To contact section does not feed through to the other apps.