Edit or suppress Order Confirmation email when payment is outstanding

Trying to set up a reasonable solution for issuing invoices through Shopify (Plus). It looks like I can’t accept partial payment on a draft order–a real order needs to be created first. But that triggers the Order Notification email, which is the same email that’s sent as a receipt when a customer goes through regular checkout and pays on the spot. I can put tokens in the subject line, but I can’t use Liquid conditionals to give us a different subject line for these two very different scenarios (even better would be to suppress this email conditionally–they should get a receipt when they check out on our storefront, but not when I’m just creating an order to facilitate sending them an invoice). Any recommendations?