How to add surcharge in Charge Lines to Certain Expense Items added using Debrief

Hello Gurus,

Our Field Service Engineers report Expenses as part of Debrief.

These expenses are typically not priced via price list, but instead manually the expense amount and currency is put in (Instead of Qty and UOM on the Expense debrief line) - Some of the examples are Air Fare Expenses, etc. The reason for this is (I believe) the company pays additional amount to travel agencies, etc. and so we wanted to be able to apply a surcharge for these expense items - like a 5 or 10% surcharge, etc.

Is there a way to do any of the following options: