A couple other things to try:
1) If the opponent only has your leg in their hand and not wrapped deep in their elbow (for instance if they caught a leg kick), you can sometimes just turn away and kick your leg out (turning towards your opposite side should twist the foot and weaken his grip allowing you to just pull your leg out). Just beware that you will momentarily turn your back to your opponent so you have to be ready for them to try to chase you down.
2) If the opponent has your leg deep, if at all possible you want to place the shin of the trapped leg to the outside of your opponent's thigh (on the side they are holding your leg), and get your hips back (like FlatsFarmer said) and down to make it harder for them to drive your though into a double, step in and sweep your supporting leg out, or pull your leg to the inside where you are really in trouble). Once there:
-pushing down on the back of their head and framing can be a good defense and can often facilitate the "turn away kick out" defense I mentioned above
-instead of just wizzering (which is a good defense) put in your wizzer but also reach down and grab your opponent's far arm right at or above their elbow and then quickly reach down and cup your other hand over your wizzer hand from the outside (assuming they have the leg held with both arms). At this point your wizzer arm should be under both of their arms cupping their far elbow and your other arm should be over both of their arms cupping your wizzer hand (and thus their far elbow). Once in this position pull up with both hands on their elbow while simultaneously picking your trapped leg down. This should result in an armbar effect and cause them to want to let go of the leg; at which point you will end up with both of their arms trapped under your wizzer side armpit. The easiest tradition from there is to arm drag to their back on their far side.
Hope this helps.