True profit on serial numbered items

Hi

I have a customer who is using stock and serial number tracking. THe cost price of the individual pieces of stock of the same item can vary as can the landed costs associated with each item. When they sell out the items, they will assign the correct serial number. However the standard system works on FIFO or average costs and therefore the default cost price associated with the individual sale is not the true cost of that unit of stock which can be traced by serial number

Example:

Buy 1st unit (SN AB123) @ 100.00

Buy 2nd unit (SN AB124) @ 75.00

Sell SN AB124 @ 100.00

profit on actual item 25.00

system calculated profit 0.00 based on FIFO

What the customer is looking for is a solution to work on true item cost both when looking at profit per transaction and within the P&L. THis must also include landed costs.

Does anyone already have a solution developed for this?

Regards

David