How to setup third party in procurement contracts, if they are not needed to be setup as suppliers

For a health care client, we have case where we need to have procurement contract with cleaning agencies, real estate companies. These cannot be setup as suppliers as they are not supply chain suppliers of health care products. For client, truly they are third parties and not suppliers. So cant define these companies in supplier master, as the count of such third party service provider will be more.

In procurement contract type we have seller role having three options as supplier, employee and third party. So tried using third party as the seller role

However what this third party is tied to, depends on the contract role sources. In role sources for buy intent source, we can tie this third party to any one of the following: all eligible customer, business unit, Customer, Employees and contractors, internal party, partner and supplier.For our use case we cant use all eligible customer, business unit, Customer and supplier. So the only option is employees and contractors, internal party, partner