ADD A 'CREATED DATE' FIELD LINES IN TO CUSTOMER PRICE PLANS

we would like to have a 'created date' field in customer price plans database with a date that the each line item was added to the contract (this is different from the start and end date fields that already exist which goes to activate/deactivate \ pricing, this is a 'created date' as in the day an item is first added to a contract. We would like it to be a field we can pull out in reports as we would use it when running contract cleanup; if a line on a contract was not ordered based on the date it was created or added then we would remove that line from the contract.