Suggestion on Intra and inter company process

Hi 

I have a requirement where we are configuring both intra and inter company billing thorugh one sales doucment type.

Intra :Process:

ORder ---> PR/PO ---> MIGO--> MIRO ---> Delivery. ( Between same company codes)

Inter Process

Order ---> PR/PO ---> Order ( supplying company) ---> PR/ PO ---> MIGO--> MIRO ---> DELIVERY---> IV BILLING.

Now the question is we have same item categories and schedule lines, but for intra there is no billing , inter process IV billing will be created.

can you suggest me with out changing the item categories how we can achieve the automatically.

thanks