Had an army chum who wanted out after completing 4/5 yrs. Was told it would take a minimum of a year, which everyone thinks was a deliberate ploy to shaft said person as they had an offer to go and train as a solicitor starting 8 months later.
The army dragged their feet, trying to persuad my mate to stay even though it was obvious there was no chance and then produced the 12 month clause just as he had been accepted for a law course.
Many weeks of wrangling later and my mate had got his escape chit signed by the committee and was over the wire. He had gone back to his prospective employers who had argued on his behalf that he only needed to serve a period of notice equivalent to the period he was paid over ie one month. After a few weeks of muttering and hurrumphing they gave in and let him go.
So it does appear that if you know EXACTLY what you are talking about and are prepared to challenge the muppets that live upstairs, you do stand a chance of winning.
PS Don't quote me if you ever need an early escape chit!!