I knew it was coming...
I really don't know if it has a name, but I'll try to explain (this is if you're right hand, but I'm pretty sure it works also if you're lefty): after the SMB is deployed, keep the spool in your left hand. With the right hand, put the back of your hand on the line, push it to your right and twist it down-upwards. Now you have a loop around your hand. Place this loop around the spool (where the line is). The line is now stopped by this simple "knot". If you let the spool go, it won't go anywhere. If you have to ascend, recover the line, and repeat the operation.
Back on board, undo the line, and untie the knot(s).
Hope is clear.