Define the Install Base Instance number on a Sales Order at the time of selling

Team... does anybody know a way to specify the Install Base Instance Number when creating a Sales Order?

The item ins Non-Inventory, Non-Transactable and, as such, non-serialized.

We are able to create Sales Orders against this item in order to create Install Base Instances but we want to define the IB Instance nu,mber inetsead of the system defining it.

When selecting the Edit IB Details in the Actions button of a sales order line, the only option in the field Install Base Number, is to selecto from a LOV instead of allowing us to specify what IB Number we want.