Best Practice for unpaid External Employees

We are currently on Oracle on-prem EBS (version 12.2.7). Core HR and Payroll (no OTL)

We have a group of employees from a parent company that will be embedded in our locations and will need HR records. They should be able to enter expense reports and be transacted upon with HR Self Service but we do NOT want them to flow through payroll since they won't be paid directly by our company. We initially set them up as a separate 'External Employee' person type to be able to access iExpense but this has caused many other headaches. Does anyone have a suggestion on best practice to set up a group of employees in this manner?