PO Line Level Approval without revising PO & Requires Re-Approval

Business scenario: On certain Purchase Orders business add 5% allowance. i.e. if a PO is for $100,000 second line for $5,000 (5%) is added. Making a total PO amount $105,000. This helps business to not go for approval chain again with the higher management for small amount and buyer can use from the allowance amount. The 5% allowance amount is already approved within EBS PO Approval, but business want to put an additional check, where certain group of people should approve this allowance before utilizing it.

What are the options to have this additional check being taken care within EBS?