PO Approval Workflow customization

I have two buyers and five directors. If anyone of the buyer submits the PO, it should go to a director based on the account segment combination in the PO charge account.

It needs a workflow customization. I created a lookup with director name and account combination.

Workflow should look at the po charge account and get the director from the lookup and send it to the right director.

Are there any other approaches that can be used.

Thanks in Advance!