If he has both underhooks, you're generally in trouble. What I've been doing, and it's been working against guys my size, is to slide my hips out and turn him over. There's a kick-up move that my coach has been trying to get me to use, but I'm not quick enough to make that part effective yet.
There is a move I use and I'm not sure but it sounds similar to what you are talking about using.
What I do is get both my hands in there (like I normally would for a shrimp escape) and then push off to make a little space. I'll shoot and underhook under on the outside arm side deep as I can. Once I have my underhook I'll scissor and roll into them using my underhook and head to drive them back (head to chest), which rolls them over. Is that close to what you are talking about??
Another one that I used on some of our Judo guys is getting the arm under and scooping a leg...keep driving into them until I feel them push into me hard trying to drive me down. When they push into me I turn hard away, lift as hard as I can with the leg, and bump all at the same time. It's a power move, but it works as long as the guy is close in size...I've actually done it to several guys that have 50+lbs. on me.