Customer Lookup Based on Order Criteria

I am looking for suggestions on how to structure the following business requirement:

If an order is for a subscription-item, create/find a unique customer in NetSuite. Otherwise, if it is for a regular, nonsubscription-item file against a default customer in NetSuite.

This client has multiple NetSuite subsidiaries and multiple Shopify stores. If a customer crosses stores for subscriptions, they want to still keep/match to one customer record.

My initial plan was to update the primary/secondary customer lookup criteria on the customer add flow, but I realized all the values to filter on are for NetSuite Record (customer, transaction, etc) values, so there is not a field to tell me if it is a subscription or nonsubscription order at that level.

Currently, the only other solution I can think of would be setting up an input filter expression in the customer add or order add flows that looks at Shopify Tags. If the tag indicates a subscription order, then it passes through the actual customer id/info otherwise it overwrites the customer id to the internal id for a default NetSuite customer.

Has anyone dealt with a similar requirement or have alternative suggestions for how to simplify the solution? Happy to add more details or screenshots for clarification as well.