Can't include Custom Contact data in Ship To address on Vendor Purchase Orders

Can't include Custom Contact data in Ship To address on Vendor Purchase Orders

I'm hopeful someone can help us with an issue on Purchase Orders.
To start with we are a reseller of goods and we must provide vendors with end user data (Contacts) on every purchase order.  We have to use the 'ship to' address and need to append Custom Fields 1, 2.. to this.
We can't get these customer custom fields to migrate to purchase orders.
We put them in and nothing comes across.

Is it possible?