A while back, I read about a study that described suggestibility as a stable property, one that didn't usually change. However, they were able to increase it by cheating.
The hypnotists planted a suggestion in a subject with limited suggestibility that he/she could see colors in some white lights. The lights were electrically set up to change from white to colored. This "success" reportedly increased the subject's suggestibility, by increasing his or her belief in hypnosis.
Short of a rigged light board, a simpler method of "cheating" might be to start off with an easy suggestion, or to confound hypnotic and non-hypnotic effects. An example of this confounding would be those who wear and use 24/7. Unless the hypnosis worked quickly, they couldn't tell whether incontinence was achieved from hypnosis or behavioral methods. Incontinence seems much more cheatable than say, hair growth, which is why this post was made under Diapers and Incontinence.
Has anyone tried this? Did it work?
(Edit)
In hindsight, a more common example would be the inductions that instruct the subject to try to open their eyes (Elman's) or try to move their arms and legs (Cardigan's). Trying a little might amplify the illusion, but trying earnestly might cause movement, dispelling it.