Is it truly possible to produce a permanent, instantly accessible flexibility that requires no warm-up or any other preparation?  

I assume that by exercises you mean stretches. If not, if you mean other exercises, then Science of Sports Training will answer your question. Concerning stretches?do dynamic stretches similar to the movements in your sport. Do those isometric stretches that resemble positions at which your range of motion is less than required in your sport. For example, stretches 1 and 3 on pages 68 and 69 in Stretching Scientifically would help for baseball pitchers. Gymnasts or kickboxers may pick any stretch from pages 70?72, plus any stretch from page 74 and any hamstring stretch from page 75. Stretches you do for the front of the thigh and for the hamstring you can later replace with front splits (page 76 in Stretching Scientifically) as your flexibility improves. You can do relaxed stretches similar to your isometric stretches or whichever ones stretch your tensed muscles.

The proper sequence of stretches in a workout is: dynamic, static active, isometric, relaxed. You do not have to do all these types of stretches in a workout. You can skip the ones that you do not need but do not alter the order.