Well, DON'T do what I did... that is, start a PhD. I have to write the longest, most boring paper of my life in order to finish what I started.
Truly, I'm in the same position as you... the only thing that is capable of kicking me in the ass is a DEADLINE. Once I have a deadline, then I can kind of work. But it's still usually at the last minute, and try as I might, 23 years of being a student (I'm 28) has not changed that aspect of my personality. I've long since accepted it as just who I am, and I try to work with it instead of against it.