How to add post processing lead time only for independent demands?

Hello,

We have a business process where the sub-assemblies that we make are either used by the assembly line or are sold to some of the customers separately.  So in ASCP, we get both dependent as well as independent demands for sub-assemblies.

The packaging time for direct ship orders is 2 days and hence we want to offset planned orders pegged to direct sales orders by 2 days i.e if the sales order is on day 10, we want to create work order on day 8. However, since the sub-assembly orders which are consumed internally (by main Line) do not have such post processing lead time, we can not define any post processing lead time at item level OR an offsetting operation at routing level. ie. if the dependent demand is on day 10, we want to create work order on day