Cost Rollup exclusion

Hi,

How can we exclude the changes of item cost (Slow moving inventory cost) in rollup. They want to include the existing cost but they dont want new cost.

Example: A is make item, Under that B,C and D are components. D is sub assembly and E,F are the components of D.

Business trying to do annual rollup, requirement is they dont want to include cost changes of D in to A. D is SMI item here.

As of now Assembly  D cost is $20 (E-5,F-15), Component E cost is changing from 5 to 6.

If run the rollup now, rollup should exclude D and existing cost ($20) of D should included in Assembly A.