This isn't all that crazy of an idea. And, with respect to those who have said this won't be a true hefe or that it is a witbier, that just isn't true, although I can understand why they may think so at first.
To make a hefeweizen, you typically use at least 50% wheat malt and the remainder (50%) German pilsner malt. For a witbier, you typically use 50% unmalted wheat and the rest pilsner malt and the. Add coriander and curaçao orange peel. Additionally the aroma and flavor profile is quite usually different as a result of the yeasts used. There are also more distinctions as is evident by the BJCP guidelines.
The contention most people seem to have with using WLP500 is that you won't get the typical yeast contributions. Specifically and from the BJCP guidelines are,
"Aroma: Moderate to strong phenols (usually clove) and fruity esters (usually banana). The balance and intensity of the phenol and ester components can vary but the best examples are reasonably balanced and fairly prominent."
That said, you can adjust the esters and phenols produced by WLP500 by altering the few ration temp and pitch rate. I just finished a blonde ale made with this yeast that was underpitched and fermented at 74F ambient and got a moderate banana and clove presence. So, if you have this yeast on hand, I would suggest trying it put. I think you'll be very happy with the results.
Also, refer to the White Labs Belgian Yeast Chart: http://www.whitelabs.com/beer/belgianchart.pdf