Good God, this is not complicated! Its about communications. Want to leave the APU and air on?... "OPS, We still have the APU and air on, please contact the ground crew and tell them NOT to hook anything up"........As a back up, put your safety vest on, go outside, talk with the lead--and tell him/her not to hook anything up...a simple 2 minute process...And if you really want to get jiggy......As you leave the gate, let the gate agent know "hey, I've contacted OPS to tell the gound crew AND told the ground crew myself not to hook up anything as the APU is running with air. Can you please tell the incoming crew this, thank you."