We've included a vacuum in our puncher prototype mechanism. So far using a shop vac we've found that the boulder lends itself well to vacuum suction for maintaining control. Also if you get the vacuum over the pinhole, it sucks all of the air out of it and makes your boulder look like a brain or a raisin.
https://youtu.be/f24bk-4sZCo?t=54s So that's fun.