Aye, auto-suggestion is a good thing. But doing it half-hearted is as effective as trying to run through a wall while awake.

Something I tried myself and it seems to work most of the time is to set up your alarm clock to real early in the morning, even if you don't hear it it won't be necessary - you just need to believe it. Then struggle to fall asleep as quickly as possible, always believing that you need to get up real early to do some annoying task.
This allows me to wake up several times during the night, even before my alarm clock rings. You can tweak this to fit your personal WBTB requirements.
The eventual worry about waking up early should keep waking you up before the alarm clock rings. This could be either a good thing or quite annoying, depending on what you're using it for. I myself found it to be great to dream recall.

However... I don't recommend doing this when you really do have affairs in early morning, as the struggle to fall asleep will eventually keep you awake for quite a while. (plus the times you would wake up later on, which would totally ruin the good night's sleep needed to get up early)