Preferred solution: Flag items as dropshipped by a custom fulfillment service
In Shopify, you can configure a "Custom Fulfillment Service" which will automatically classify items assigned to that service as "fulfilled by email" in Shopify.
Once this is configured and items have been assigned to this fulfillment service in Shopify, all new orders for these products will appear in SKULabs as fulfilled by that service.
You will still need to configure SKULabs to now classify this fulfillment service as a dropshipper in your Shopify store's settings within SKULabs.
Alternative: Flag items as virtual / digital
As an alternative solution, you can uncheck the "This is a physical product" checkbox in Shopify (requires_shipping false in the Shopify API) and they will automatically be excluded when found on new orders going forward.
How to hide empty orders from appearing in SKULabs
Please note that SKULabs will not adjust inventory for dropshipped or digital items in SKULabs. Please reach out for help configuring deduction for dropshipping and digital items.