Hypnosis could actually be the best way to "cure" people of daydreaming... As daydreamers who use kinesthetic movements to fall more easily into their daydreams, we are actually hypnotizing ourselves to not see the world around us, but rather the world in our minds.
Ergo, we are significantly susceptible to hypnosis, and if one had a hypnotist to hypnotize them to no longer daydream, it might actually work.
I've heard of people being hypnotized to stop smoking, lose weight, get over a phobia, etc, however those people are only affected for a short amount of time usually. Maybe because daydreamers are so susceptible to hypnosis we could use this side-effect of our daydreaming to cure our excessive daydreaming...