While derping around on Facebook and Youtube I came across two very nice videos that deal with a failed single butterfly sweep from a seated position. Both involve your opponent posting out with their opposite leg and both involve you taking control of that leg. The sweep option is really cool; you pretty much take deep half, X guard their hooked leg and kick out to a single-leg takedown. You can probably pass most of the time, too. The other option is a basic ankle lock from a position I'm familiar with because I usually hit most leg locks from there. I do have a tendency to "reap the knee" without realizing, so I have to be conscious of that and stop the bad habit.
Ankle Lock Option:
X-Guard Sweep Option: