I've heard of folks holding the loaded holder upside down with the slide pulled out and zapping it with air after loading it. Not doable in a changing tent though. Dust only shows up on your good negs that you didn't make a dupe of on location. I always make sure to remove as much dust as possible from the darkslide before inserting into the camera too. Wear a had when loading your holders if you're in the darkroom.
vinny