PO Workflow - need to assign different emailIDs for PO requesition and Po approval

I have a PO workflow setup in my system which will approve PO if the PurchLine.Net amount is less than 500 USD or send to approval if the amount is greater than 500 USD. Currently I am able to assign only one Email template which will be sent for both PO request as well for PO approval. I would like to be able to send the appropriate email (for request - request template and for approval - approval template). I am not able to figure out how to do this through configuration or through code. I am looking into SysWorkflowMessageQueueManager and Tutorial_WorkflowProcessor code but of no help. Please help.

Thanks