How to delegate approvals to other employee - only for direct reportes expenses

Hi,

Ours is emp and supervisor approval hierarchy.

My client CFO would like to delegate expense reports approvals to  secretary for those who reports directly to CFO. Rest all type of approvals wanted to keep with CFO. Is this possible on standard functionality? if yes please let me know.

I have below in my mind ....

If I create Vacation rule on specific item type 'expenses' and delegated to other employee then manager subordinates booked expenses in iexpenses will go to approval for delegated employee ? is my understand correct on the delegated process.

Can suggest on this...

and rest all the type of i.e. PO / PR/ Purchase invoices approvals etc., type of transactions approvals remains with  Manager right...because employee doesn't want to delegate all type of transactions approval. Only wanted to delegate employee expenses who are reporting to him directly.