anything that is in contact with the bar changes something, down to the smallest ammount of dust. The closest thing I've seen is this wire system, the DBs or BB is on two wires, on the bar you have to hold inn this pin, if you let go of that pin the BB/DB will get locked on the wire. But even the wire makes a difference, somehow.
You could make something like air shooting up with the exact ammount of force to keep the bar in place, or some sort of mechanical device grabbing the bar, that reacts to some kind of sound or whatever. But let's remember, it's also a cost question. If you design something that costs as much as a spaceship, no one's gonna buy it..
and I diden't get your examples at all.. If someone want's to make a childrens scooter, fine by me, just don't mess with my weights. And a Segway wouldn't be the same by far.