Scuba for rolling
Saw at The Dash Point Pirate that he (Andrew Elizaga) had met a paddler with an unusual ambitious attitude towards rolling. He had built a SCUBA-apparatus to assist in his learning to roll - he put a small air tank in the day hatch compartment of his Chatham 16, and with an air hose out of a a custom hatch cover to a mouth piece held under the bungees on the deck, he could stay underwater a very long time. Thus he could take his time, concentrate on technique and not have to worry about coming up for air.
Slightly more down-to-earth are those ideas I have seen or heard of, with a hose, as a crude snorkel, down inte the kayak, or a mouthpiece attached to the foredeck, so you can bend forward and get a little air from inside the the kayak before a new rolling attempt.
To me there is a basic flaw in those ideas. You do not learn how to roll by spending more time upside down, or by hanging upside down, analysing the paddle movement. You learn to roll, with or without assistance, by learning how to coordinate the moving of the paddle, body and kayak to make the most of gravity, inertia and floatation. Hanging static upside down means not using the inertia and having a less favourable setup for the next attempt. A competent roller that for some reason miss a roll, usually switch side to use the energy from falling back into the water (except of course in high winds).
Even a less lucky roller with limited lung capacity can make two or three attempts before running out of air - most break off prematurely for fear of running out of air. If you cannot pull off a roll on the first or secong attempt, chanser are that you will not succed.
Handling those extra gadgets also takes focus from the rolling itself, which I believe is a disadvantage for those learning.
The basis of a reliable standard roll is not very complicated: use gravity to gain speed down into the water (this part usually comes easy ;-). Lean aggressively forward, forehead and paddle against the deck, to use inertia and to avoid impeding the rotation - thus you reach the surface before starting to move (getting three fourth of the roll done for free). Lay back down in the water and float in over tha kayak with neck close to the deck, while the floatation still keeps you up (note that with practice you can keep this floatation as long as you wish). With one hand at each shoulder the paddle does its part without you having to consciously control it.
A common beginners mistake is to sit up or wave the paddle before reaching the surface, thus stopping the motion and ending up in exactly the unfavourable setup position that the inventions mentioned initially assumes.