dallinsmommy... Liam sort of did it on his own due to us being out & about with activities for his big brother, he didn't demand a feed or would sleep when he was due on a 3 hour EASY, so it just sort of worked out that it happened.
But with my first, which was where I discovered about big babies & snacking, I had to let him whinge it out for a while... I would do things to distract him, walk around outside etc or give him a paci to extend him out, I really can't remember how long it took, it took place around 4 months for him & I just made sure I never fed in less than 3 hours & mostly 3.5-4 until he got there. It is also important for the sleeps to be good, I know there was a stage where I did EASASE, so there was a gap for activity, but no feed between 2 45min naps... I occasionally still do that with Liam, as I know he doesn't wake from a 45min nap due to hunger.