Compressed air directed into the space between the rubber and the steel works instantly. This works for removing /replacing hand grips as well.
Put one hand on the outer end of the footrest rubber or grip and apply a bit of pressure in the desired direction, either on or off. Aim the air nozzle at the inboard end of the rubber and depress the valve. The blast of air will temporarily stretch the rubber to maybe 15 or 20% larger in diameter at which point thegrip/tread will literally fall on/off. The air nozzle needs to be right close to the end of the rubber, perhaps an inch or so away. Sometimes it takes three or four blasts or air to get the item on or off, but it is all over in seconds.
Shown to me by a kid working in a bicycle repair shop!
on edit : I put a handgrip on this am using the above method and realized my info is slightly off. I wrote " The air nozzle needs to be close to the end of the rubber, perhaps an inch or so away"
In reality the air nozze needs to be pressed right up against the rubber and aimed at the area where the inside dia. of the rubber meets the outside dia of the handlebar or footpeg iron. Slide the rubber on or off with the air nozzle depressed and moving as a unit with the rubber.
Glen