How to generate a customized work order number based on work order type

Hi,

     We have a requirement to generate a customized work order numbering based on the work order type. For example, if the work order type is accident, the WO Number should be like A01/A/0001, where A01 is the Org code, A Stands for Accident and 0001 is a running number.

The Prefix A01 can be set at EAM parameters and the running number can also be left to system generated. But how to insert the alpahbet A if the work order type is Accident.

Because the system generates the work order number as and when the self service screen opens after we hit create work order button. It does not wait till we keyin the work order type.