By doing it externally by locking the water molecule into place with some form of radio waves. Maybe forcing the water molecules to align and be held in stasis while the temperature is lowered.
Something that penetrates the body without harm. One form of EM is an xray another is what happens in an MRI with a mag field. Both types interact with the human body and cells directly. Well maybe an xray is not a good example. A microwave is tuned to the water molecule and causes the molecule to jiggle randomly. How about a more organized, nonrandom molecular movement.
In other words, use some kind of EM source to prevent the water molecule from transitioning.
Like a Star Trek tractor beam? You might as well speculate about transporter technology. Pure science fiction.