It's a tough one. Is your class very interactive? Hands-on? I know the WIIFM only goes so far when nature says "hey, need to get some rest here!!!" Most of the courses in our programs are pretty interactive which help. Also, we have had quite a bit of success with classes who form a quick bond and help one another through. I've found some of the students are very creative and competitive. They set the bar high and help keep one another motivated etc, even for such inexpensive things like having a pizza party if all the class makes it through each 20-day course together and passes all the tests & lab assignments without turning any in late. It's amazing what the students do for retention - all by themselves. I totally agree with using an outrageous and/or humorous approach at times just to keep them on their toes. (When I used to teach.)