Hi @hangel88 ,
Why not create a draft order or an actual paid order with Shopify at the time you ship the impression kit? Yes you definitely can use an app to fill in the gaps. It seems the real problem is the customer isn't directly placing an order in Shopify. We would like to take more time and get solid idea how far you've come and how we can help you.
Please contact us here at firstname.lastname@example.org to discuss more about a potential solution