You can also pull a "crawfish" wrestling escape/reversal if your opponent has his arms wrapped around you in a gutwrench, or by around your head if you have an arm in. Simply put:
1) Reach back and overhook you opponent's arm on the opposite side. So if your opponent's arms are in a gutwrench, if you are overhooking his right arm you'd do it with your left, with their elbow in your armpit and grabbing their wrist.
2) Lift your base by tri-podding up off your knees. You need to create space for what you are going to do next.
3) Once you have some space, shoot your free arm through the gap while you sit-out on the same side. So, if you've hooked your opponent on your left side, shoot your right arm across while sitting out on your right hip.
4) When your head clears the gap under your opponent's left arm shoot it up and back to lever them down onto their left side. Once your clear, you can do a few things:
A) If your momentum is really fast and explosive, you can continue around until you are on top and the positions are reversed.
B) Shoot your right arm in to their waist, turn into them and drive to end up in cross-body, or rear-cross body if they don't react fast enough.
c) Shoot your right arm in to their waist, turn into them while grabbing them on the far side of their back with your left arm and pull yourself onto their back.
You can also cinch a figure-4 grip while you are under, and try to sit out into an armlock. It is actually really easy to tweak their arm if you choose that.
As an example of what I'm talking about, I have this Vid of the Bob Sapp/Big Nog fight here
. At about 40 seconds in (after Big Nog gets dropped on his head) he goes for the escape from the position your describe and isn't fully successful. At 1 minute and 50 seconds in, he goes for the escape again and gets it, landing in side control. Although they don't show it in this vid, he does the same thing to popout right before he secures the armbar on Bob to win the fight.
I hope that helps.