Make it easy!
My PT had a suggestion for my "difficult" (read "near impossible") 4th year class yesterday. Sit them a test shortly, but make it really easy. Ensure they all get decent marks.
Why? Psychology. If they get a good grade it might make them sit up and think "Hey, wait a minute. Maybe I can pass this course after all". Of course, it may make them think they can afford to slack off...
It's worth a shot, though, and I'll be giving it a go next week. Fingers crossed!