This is a major shortcoming of the Baan IV standard. The detailed information contained in the standard cost price structure of standard items (concerning material and operation costs) gets lost as soon as this item enters a project. There is no work-around in the standard.
However, I have realized a customization implemented for two customers of mine. However, major sessions have to be changed (mainly the project cost price calculation sessions), to not use cost price component of a standard item, but a more detailed information instead. If it's feasable and how long such a customization would take, depends on your situation (depth of BOMs, number of orders and so on.), because e.g. the number of integration postings will increase.
If you are interested, you might contact me using the data given below.