theres a couple ways. one is you have to grab his "pushing leg" and step back with the leg that isn't hooked and step behind your other leg as you sit back trapping his "hooking leg". once here change the angle on your shin by shifting your hips, and throw his other leg over your head and hug around the leg your attacking with your arms as you roll into slicer position
now i'm usually pretty good at describing techniques, but this one is particularly intricate, and is not easy to learn with an instructor, let alone over the web. you're going to at least need to find a video.