Populate Custom Fields 1, 2, 3 with Product Attributes?

Is it possible to auto-populate the custom text fields with any kind of information, or can you only manually add info into these fields? I am using ShipStation for Etsy but there are no Etsy SKU numbers for each product variation so the only way to identify the product is by using the item attributes such as "Size" and "Color". There is no column which shows product attributes but they can be seen under order details so that information IS being passed along by Etsy to ShipStation. Can ShipStation dynamically populate the custom fields with my product attributes for each shipment?

If not, then could ShipStation automatically copy each shipment's "SKU" to "Custom 1"?

Thanks.