Because he's been up so late for so long, this might take some time. Once he does crash, how late does he sleep? Does he take a nap?
Sleep has never been my strong suit, so I can somewhat relate. And I definitely feel your pain.
As you try to get into a routine that will be easier, I would plan lots of very active things to do. Go to the park, the zoo, the mall (do they have a soft play area?), McDonalds. Basically anything to keep him really active. Also, being active will help you to stay awake!
Make sure to have a good dinner. When it's time to settle down really set the scene. Turn the lights down, turn off all electronics. Have bath time, pj's, brush teeth, snuggle on the couch are read a couple of books. Let him know that after the books it will be time for bed.
It's ok to lie down with him (well, not everyone will agree, but I think it's perfectly ok). Actually, I prefer to sit down on the floor next to the bed. Sometimes I sing, sometimes I pat my son's back. Actually, I don't usually need to do those things anymore, but I used to. Now I sit against the wall and read my Nook (love having that backlight!). Once you really get a good routine and he's used to it you really won't need to stay with him. Just say goodnight and leave.
Give it some time. It's going to take some tweaking, especially the timing of everything. Try to keep the order of events basically the same.
If he still takes a nap, try to make that a priority, as an overtired child is so much harder to get to sleep.
Try a plan for a week or so before making any big changes, as he will need some time to get used to the routine.
Hang in there! You will find something that works.