Do a test run using peanut oil as your frying oil...and using "the icing" of infused duck fat (as fishscale28 mentioned) for a finish...much like truffle oil fries.
You get the taste benefit (hardly the cost) of the duck fat...peanut oil does the heavy lifting.
If you like it...careful with the wording on the menu as far as being all-in about "duck fat fries" You can frame it the same way truffle fries are written on a menu. Tossed - finished or drizzled with...insert the description of the infused duck fat.
Here's an example...http://www.fatcowburgers.com/menu.php
post edited by CCinNJ - 2013/03/02 10:47:29