How to use PO Acceptances without using iSupplier or creating user accounts for supplier contacts

We want to use PO acceptances - signature required setting. We will not be using iSupplier.

It appears the intended functionality is that PO signature acceptance function cannot be used without iSupplier.

However, in another instance that we have access to from an acquired company, they are using PO Acceptances, with Signature required, exactly the way I hoped. PO Option is set to default to signature required. The users submit the order for approval, and it goes through the appropriate approvers. When it reaches the final approver, the status is set to Pre-Approved, and the order is sent to the vendor by email. From there, when the buyer receives the acceptance offline, they will add the acceptance info manually, in Tools > Acceptances. Then the workflow proceeds and the