Material Ledger Roll up of Expense to material

We want to accomplish following scenario.

We incur variable expense on finished goods and we want to add that expense back to the material as part of Material Ledger at end of period.

Ex Finished Good - $10

Var Exp - $2 ( Lets say shipping expense)

I want to add the $2 back to fisnished goods, when we sell to customer.

Will be helpful if you can point me right direction.

Regards

Jyampi