Setting the Expense Account on a Purchase Order

I am trying to implement a Purchase Order process for my company.  We are going to use the PO's mainly to keep track of expenses for which we need to accrue. I understand NetSuite is not currently set up to do accruals directly from PO's; I plan to run a custom report that gets the data and then book a JE accordingly. The thing I am unable to figure out is assigning the expense account to the PO. It seems I can only add items to PO's, not general expense lines as you can in Bills. But even with the