Defining Item for Service Tax

Service Tax paid on supplier invoices is taken as input credit. 

Is it essential to define item for Service Tax as Inventory Item?  If yes, the requirement is to get the accounting for receiving from Expense Account defined at Item - Purchasing Tab instead of receiving inventory account defined at Receiving Option.  Can any one please help to define item, which is subject to Service Tax and account to default from Expense Account - Purchasing Tab.