It would be helpful to post more information on what you are trying to test, as we might be able to suggest more practical alternatives.
The boiling point of water at one atmosphere, is 100 degrees C, so without heating it in a sealed container, it couldn't be done easily without boiling off all the water, hermetically sealed rxn vessels are NOT reccomended though, as if it explodes on increase of pressure, you not only have container fragments going off in your face, but boiling NaOH, which from past experience, I can tell you, isn't really a pleasant experience
One thing you could try, is microwave heating, as microwaves are able to superheat water, so long as the surface isn't disturbed, although I would do this *only* while wearing suitable face, eye and body protection, as well as thick gloves, and preferably, handling at some distance, as disturbing the surface even slightly, of such a superheated fluid, can cause it to suddenly flash up in a cloud of superheated steam.
You aren't trying to isolate sodium metal are you by any chance? if thats your aim, then dissolving NaOH in aqeous solution is pointless, as any Na formed will react instantly leaving you with yet more NaOH, and hydrogen gas, so for electrolysis experiments, the hydroxide must by fused by heat from a burner or blowtorch, and kept in the molten state
Oh, and I would try aqquiring a heatproof ceramic pot of some description, for handling hot or boiling NaOH, or fused NaOH melts, as they attack most metals, and to an extent, graphite crucibles and electrodes with great readiness.