Absence approval for top employees

Hi All,

I have been trying to find a solution for top employees who don't have any manager assigned. We have multiple entities, and each entity has one top node employee, but there is no particular job or position that I could use to identify such person. We have one level of manager approval. I have tried following options, but couldn't get the working solution yet.

1. Use custom role - Thinking to assign a custom role to those employees, but there is no option to select Role in Absence Approval rule's If condition
2. Use person number - It works, but not recommended. Our design authority do not want anything to be hardcoded