Price markup and contribution margin

Hello, 

I have noticed an issue with existing Sales Parts and I am unsure of the correct way to apply a % increase to the price. Initially, I assumed I could use the contribution margin on a Sales Quotation to accomplish this, however, if the part is existing in your system, that is calculated automatically. 

The scenario below outlines the issue I am facing:

1. Existing part number XYZ has a Cost of $4.55 and a Price of $18.35
2. The system calculated Contribution Margin rate is 75.17%
3. The customer has contacted us and stated they want 255 XYZ parts expedited and they would like to see a quote for this.
4. We would like to add 20% to the price of the part for the expediting. 
5. Our Sales team created a quote and modified the contribution margin. They changed it to 20%, which dramatically lowered the price.

Modifying the CM does not appear to be the correct method to markup a price of an existing part in this instance.

Is there a function in IFS that would accommodate this scenario? Any help would be greatly appreciated.