Here's a quick and easy trick that I'm surprised more people don't know. You don't need a high-priced, high-powered electric fan to create great wind. In my experience, you can actually get better wind by two or three layers of firm cardboard together, hand held, and swooshed by the subject in a firm, focused, sweep. If you get a really high powered fan, it can get a little annoying as it's blowing everything away, but this homemade fan can produce fun shots like the ones below. My last tip though is to make sure you put a little muscle into it, using both arms for a quick, firm fanning of your photography subject.
Using a tripod or some kind of mount, take a picture of the backdrop before or after the client stands on the backdrop, and then use that as a layer in photoshop for easily removing the fan if it happens to show up in the picture (see below).