how to create BPA with multiple supplier sites ?

A BPA can be created for a specific Supplier and Supplier Site only. However, in our client's business, there is a need to create a BPA for a supplier with multiple supplier sites because of the different taxes linked to different supplier sites. This will help the requester to raise a requisition for  BPA linked item with the desired supplier site which should be one of the multiple supplier sites.

How can we achieve this requirement of creating a BPA with multiple supplier sites?

Your suggestions are most welcome.

Thanks,

Sid