Adding a % variable cost to a configured item

Has anyone added a % cost to a configured item as part of the configuration process using the other costs in configuration? The costs of the item through normal configuration may be $100 and we want to add 2% warranty to the cost during configuration to give a final cost of $102. If the item is reconfigured to (say) $150, the total cost should then reconfigure to $153.

Is this possible? Any help appreciated!