Fergs, you should post questions on the forums instead of here. Much greater chance of getting it answered.

As for your question, if the opponent just hugs your legs, their weight will be on your lower body and not your torso so he has no pressure to keep you flat on the mat. Take advantage of this by posting on the mat, sitting up, and shrimping away. In particular, if you can make a collar tie on their neck, you can use any of Marcelo's numerous sit up escapes from here, such as taking the back or crucifix, rolling backwards to take top position, doing a hip throw to take top position, etc. If you can't make a collar tie and the opponent circles around to your side you can hit a wrestler's switch to take their back or recover position (this will take some practice and is not on this website). Sitting up is a very effective counter against leg hug passes, even against larger opponents, and I think its the main reason why you hardly see black belts attempting leg hug passes.

Please note that if the top player has long arms or you aren't posting your arm far enough behind you, they might be able to grab your posting hand and collapse you back down into a proper folding pass, where their weight is on your chest instead of on your legs. This is a legitimate counter, but as long as you're aware of it you'll probably be okay.