NON PO Invoice approval routing

I have a question on webcenter imaging approval routing.

We are in the process of configuring NON PO invoices in webcenter. When non po invoice comes in to webcenter it goes to coding form where GL codes are assigned to invoice lines and up on approve invoice is created in EBS. My requirement is to add approvers to the invoice so that after coding is complete it should go to the approver for approval and once approved invoice should get create in EBS.

I found document regarding LDAP approver (document id: 162994.1)but it does not help as I need to add multiple approvers.