To do the "pressing armlock", you can get an underhook or even a deep overhook ("whizzer"), put one foot on hip and the other one on the shoulder of the arm you want to underhook. Here, you're taking both legs out of the butterfly positions.
Nice answers, this should be a saved thread.
So essentially, a lot of submissions from the butterfly guard are about threatening with a sweep, then start the submission with the legs INSIDE your opponent's legs, i.e. still in the butterfly position, and then take your legs out to finish the submission.