Warehouse Managment

We use warehouse management and occasionally have a nonstock line that needs to follow order activity rules same as a stock line type, in order to invoice all lines together.  The linetype has no inventory interface, no item #, it's just an additional line for a discount.  Is this even feasible, or should we bypass status via order activity rules?  This could be problematic as the non stock line could invoice independently if the rest of the lines haven't processed through WMS. Next status preference won't work as we don't have an item # on which to base the preference.