While it's hard to say without seeing video of exactly what you are talking about, it sounds like his base would be compromised on the side of his dropped hip. If you already have the super stomp in, which I assume you do since you are already trying to free your knee, drop your inside foot to the ground and use your butterfly hook to threaten the sweep and he will have to base that leg out and give you the space to free your leg.
As I said, though, hard to say exactly without being able to see every detail about the posish. Sometimes you just have to reset and go back to half and use a different path.
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