I would trade them to someone who wants them for the stock fenders, with cash of course, and cut the stock fenders. That way you make money and get the flat fenders you want. Plus, if you screw up stock fenders, they are super cheap as take-offs.
How much do stock fenders go for if I mess mine up cutting them.
You could also try and contact EVO or PSC since they make nice fenders and probably do a lot of installs. They both probably throw away a ton of stock fenders every year that they might just let you have...