Disassembly Cost Allocation

Hi

We struggle with the current Disassembly functionality in B1. Product A is made up of Product B,C,D. When one assembly the product is will take the individual average cost of each sub component and add it up to get the cost of the main product and when one disassembly again the product it will take the current cost of the subcompoents and just add the difference to the WIP Variance account. We need to distrubuted to total cost on the some way as it had been assembled. Any help or ideas will be appreciated