Do it like a treasure hunt, say 10 min departures or faster aircraft first to the first waypoint etc, so they actually go around a course..
You could have clues (such landmarks with a cryptic clue and a heading from that.) as an example Ford Prison could be a Car for bad boys etc.
Give them all a set of sealed envelopes with the answers in to each waypoint, make sure they cannot be read through the envelope by holding it up to the window, that way if they cannot find a single or multiple waypoints, the answer contained will get them back on the course, (points deducted accordingly), you can then factor into the final results any opened envelopes etc.