awwwww you poor thing. I also have heard amazing things about the 'baby whisperer' book and people that swear by it.
What time does he have his last feed? How long has this been happening for? Could there be other issues?
You could try giving him a dreamfeed at say 10pm and see if that helps him sleep through from then. They say that it only takes 3-4 days of the same pattern for it to become a habit so trying to change the pattern/habit means a few days of hard sleepless nights.
Another suggestion is you could also go in 10 minutes before he is 'due' to wake up at 3am and semi wake him. This 'interferes' with his sleep pattern and inturn often makes them 'restart' the sleep pattern. This worked very successfully for us when Jasmine was about 5 months. It meant I would have to set the alarm to wake myself up but I did it for about 5 days and she eventually just slept through. I can give you more advise on this if its something you would be interested in.
I do like the water idea in a sipper cup.
When he does wake up at 3am and you say you let him cry but he cries for 30 minutes. Do you stay in the room with him? Often its a good idea to actually stay in the room with your hand on their chest and constantly reassure them and therefore calming them down. I agree that it is unlikely that he is hungry but its just a habit now that he wants to feed.
hmmmm I am struggling for other advise here. Will have a think and see what else I can come up with
I am thankful that my daughter sleeps from 6.30-6.30 pretty much every night and has done so from a young age but I am on another baby forum in Australia and have read alot of advise from other mothers going through similar things to you.