I've been reading WFMW for a year or so now, and I'm so excited to be posting my very own tip!
So, if you have a preschooler who has MAJOR trouble listening but who is motivated by strange things, this is the tip for you.
Have a discussion with the preschooler after a temper tantrum resulting from not being able to go to the playground after school because she has ballet in 40 minutes (or similar situation). The discussion is about TRUST. "See, Chickadee #1, I can't let you go to the playground after school because I can't trust that you will come with me when I call. How can we build trust? I know, let's build ourselves a "trust bank".
Get yourself a formula dispenser (the kind with three wells). Label one well Neutral, one well More Trust, and one well Less Trust. Get yourself some ditalini or other small pasta (elbow macaroni would also work). Fill the Neutral well to the brim. Explain to recalcintrant preschooler that she will be allowed to go to the playground after school or other fun activity only when the ditalini in the More Trust well are more numerous than those in the Less Trust well.
Watch the behavior improve. Watch the preschooler ask "Do I get a ditalini?" after good behavior and do a victory dance when the answer is yes. It's key, however, to just add ditalini to the Less Trust well at bad behavior without making a huge production of it -- otherwise, you'll get into a power struggle and invite a tantrum.