Base Price and Markup Price

My client wants to do something strange and wrong, but it's impossible to tell a client he's wrong so I've got to at least try and find a solution...

He wants the price to be a Cost Price, then he wants to put in a fixed markup in the discount tab rather than a percentage, so instead of a minus it's a plus.
Then he can then just go in and change the base price and the selling price will change accordingly.

E.g.

Item 1
Base Price: 100
Discount: + 15

Price of product on the front end: 115.

Does anyone know of an extension where this might even slightly happen? Basically a base price and a markup value.

possibly something like this ?

Global Price Changer
http://www.opencart.com/index.php?route ... n_id=17617

found here:
http://www.opencart.com/index.php?route ... p%20prices

Ernie
openshop.li