Leo and the Dummy

Leo has been cluster feeding since day 3. He can cluster feed for 3 hours only on some days but up to 12 hours on other days. It's been so tiresome that I've been seeking for advice about how to bring this to an end and replace it with a 3-hour scheduled feeding through out the day whenever I've had a chance.
This Tuesday I went to a mothers group and asked for advice again. A mother said her baby was like that before. He was on the breasts none stop for 7 hours one day. She then got a dummy for him and it was a life saver for her.
So my DH bought a dummy for Leo yesterday. When Leo demanded for cluster feeding again yesterday I gave him the dummy. He took it immediately and sucked vigorously for a few minutes before falling into sleep. I was overjoyed and hoped that I'd finally found a solution.However the second time I wanted to give the dummy to Leo, he started to push it out. I tried again and again, but he just didn't want it any more. Finally I gave up and decided to feed him. He's so happy that he talked to me merrily for quite a few seconds, as if saying "Finally mom, you got it. This is what I wanted. The other one was weird. I sucked and sucked but nothing came out!" , before going on the boobs with great satisfaction.He continued to refuse the dummy today but he hasn't done his cluster feeding today. It's now 9pm and he's been sleeping almost for the whole day except a few very good feeding. Maybe he's decided to do a cluster sleeping for a change today...fingers crossed!