Payable Invoices Approval

Hi,

We are using the Payable Invoices Approval workflow in R12.  We have defined an hierarchical chain of approvers:

Approver 1

Approver 2

Approver 3

...

Approver 8

We would like to have the workflow doing this : if the approver 1 does not approved the invoice after a timeout, we would like the process to escalate to the next approver.  We want the process to stop after there are 2 approbations among the hiearchical list, the invoice has an approved status.  If there is no approbation or only 1 at the end, we want the invoice be rejected.

I know we have to modify the standard workflow to change the behavior, because actually, after a time out, the invoice does not escalate and the invoice is rejected.