There are a ton of setups to get to 1/4-G. I like to do it mostly from either deep half (drive the knee through) or regular 1/2 (turn to face the guy's legs, and use the elbow of your far arm to free your knee so you can keep the same arm underhooked. If you get good at this, though, you can actually bait it from mount if you feel like you are not getting anywhere. I forgot about the Samurai until this video, and have been hitting it about 4 times per hour of sparring since. Awesome!