Sometimes when you find yourself in 1/2 guard, you may wish to move to butterfly guard. You could always go with the traditional shrimp to bring your other leg in - or you can try this method. Here is a quick video of the technique, the step by step is below that.
Eddie has me in his 1/2 guard
Eddie folds his right leg tightly over my right leg to keep me locked into his 1/2 position, he then puts his left foot on the ground to position himself deeper onto his right hip
Now that Eddie is on his hip, he lifts his left foot up off the mat and...
Eddie inserts his left foot into my right hip
Pushing with his left foot, Eddie can now pull his right foot between my legs and claim his butterfly guard
Eddie finishes in butterfly guard