I have had good luck with Cascade in Witbiers for both bittering and flavor/aroma. I don't brew German wheats, but I don't think you'll have a problem using it for bittering. If you want to minimize the Cascade character, just add it at 90 minutes - the extra half hour will help boil off most of the aroma and flavor compounds.
In the future, you may consider buying a pound of a clean, flavor-neutral bittering hop like Magnum, Warrior, Horizon or Galena and use it for all of your beers. It'll save you money in the long run if you can store it properly (preferably vacuum sealed in a freezer)
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Primary: Saison, Berliner Weisse, sLambic I, sLambic II, IPA, 70/-
Secondary: Orange Blossom Mead, Flanders Red I
Kegged: Fat Man Porter w/ 1469, Fat Man Porter w/ 005, Centennial Falcon w/ Conan, Centennial Falcon w/ Denny's, Barrel-aged Fat Man Porter, Belgian Dark Strong, Dark Mild