Ｐｅｒ diem expense for manager approval

Hi Experts

We have used per-diem expense type in i-expnese.
We have an issue with per-diem expense.
Please tell us the method that we can submit Approval Request of expense report with only per-diem to manager.

On our setup, When a expense report only for per-diem ts submitted, the status of expense report become "Pending Payment Approver".
This means that maneger can't receive the approval  request and can't approve it. 

When a expense report is submitted, in our company, Approval request sholud be submitted to Manager,anytime.

How can we do it?

Or Can this not be realized by the standard function?