How can I use a project attribute in procurement approvals?

My customer has a requirement to direct project-related P2P documents to approval based on an attribute of the project - basically corresponding to a combination of line of business and sector.

For example, if the purchase is for an infrastructure project in the Nordics it should go to one set of approvers, and if it's for a power line project in South-East Europe it should go to another set of guys.

How can I achieve this with procurement approvals?
This is not information that the requester or procurement agent knows so it can't be entered or selected on the document. They know the project, so this has to be derived from the project that they enter on the document.