You may hate me for saying this, but I'd cut caffeine after noon (or entirely) and see if that has any effect. Also, you may want to look into setting up a more vigorous workout regime. Your body most likely has excess energy (much like mine) not yet burned by the end of the day. Another thing that can work is making dinner a small meal (again, the energy thing) and consuming more of your calories earlier; big breakfast, moderate lunch (eat more if you're sluggish, less if you're still sated from breakfast) and a small dinner. These are all things I *need* to do myself (except the caffeine thing; now that I'm not at VSoft, I'm not ingesting any caffeine), so don't take it as judgemental.
I didn't specialise in disorders so I can't comment on your self-diagnosis, but I could write pages on things you could do to affect your sleep. Another big thing that people tend to discount is light. You probably don't notice that I turn my lights lower (or use the lamp on its lowest setting) in the evening. Your body's seratonin/melatonin/etc. levels are affected by the amount of ambient light. Melatonin especially is inhibited by light, and it's a very important part of the hypnagogic cascade (falling asleep). I like to sleep with my blinds open at least partway and I turn all my lights on superbright in the morning to stimulate the reverse process (inhibiting melatonin tells my body to "wake up"). I can't stress the importance of natural light enough for keeping your body's rhythm(unless it's winter and you suffer from SAD). And, interestingly enough, light affects melatonin production in rats just as it does in humans, but the effect of the melatonin production in rats is to induce wakefullness, NOT sleep. So if your schedule is off, taking Melatonin supplements may not help, because you CAN reverse the effect it has on your system through training. The jury is still out on melatonin's effectiveness as a sleeping aid.
In a certain sense, the body wants to go to sleep later each day. It's light which resets the clock. In "free run" experiments performed in a cave away from sunlight or even the heating/cooling patterns induced by the sun, on average most subjects fell into a 28 hour day rhythm. So I'm not sure about this syndrome. It suggests that the subjects fall asleep at the same time each night, but I'd be interested to see free-run experiments with subjects suffering from it.
Good luck. I've never had "normal" sleep myself; I've been an insomniac most of my life. So if you find success I'll enjoy hearing what brought it on (in addition to envying your delicious REM cycles).
So, in short:
+ Exercise. Preferably earlier in the day (you don't want to exercise less than 2-3 hours before bedtime)
+ Diet: Cut out caffeine, and if you can, cut down on sugar. Especially in evenings, on both counts. Big meals in the morning to progressively smaller throughout the day.
+ Light: Bright lights in the morning. Wikipedia agrees, if you look under treatment for DSPD. Dim lights in the evening. In addition to lowering your electric bill, you need to give your body time to start manufacturing sleep substances. It sounds like if your phase is disturbed that instead of melatonin saying "SLEEP" to your body, it's saying "SLEEP in four hours"; you're stuck between full nocturnal and full diurnal. Again, give your body time to start falling asleep. Start around 8pm, which is sunset around here anyway.
+ Regularity: You need to enforce your sleep schedule. Tell your body who's boss. This will most likely work with all the other steps; not so well on its own. In bed, lights out, by 10. If you can't sleep, meditate. Avoid stress in the evenings. You should be totally relaxed by bedtime. If I can find my progressive relaxation tape, I will make a copy for you. If you can work on reducing your stress and anxiety levels, you'll have a lot more success sleeping (if you're anything like me). Relaxation must be physical as well as mental.
+ Acceptance: Some nights, you just won't be able to fall asleep. Stick with it. Keep it regimented, whatever schedule you set, stick with it. Get in and out of bed at the same time every day no matter what. And don't do anything in bed except SLEEP. Just like rats, Pavlov's dog, etc., your body can be trained. If you train it that bed = sleep, even the very environment of your bedroom and the act of getting into bed will initiate sleep mechanisms in your brain. I am, BTW, the WORST offender at this. It's one of the reasons I prefer a 1-BR over a studio. Bedroom = IT IS CAN BE SLEEP TIEM NOW? rather than the place you do every single freaking thing ever.
Sorry for the summary longer than the original comment. Like I said, best of luck. (Told you I could lecture on this for days... I really need to look into work at one of these sleep labs once my debt is paid off. Not sure if I want teh gradd skool, but I sure as hell miss the SCIENCE! of it all)