There are some cabinets that do just that - maintain a pan of water. Yes, it helps - but evaporation alone may not be enough to sustain the appropriate humidity levels (70%, +/- 10%). In larger spaces (cellar), you can rig a humidifier by placing a towel into a bucket of water and hanging over the side down to a level just below the bottom of the bucket. Allow the towel to drip on to a concerte block.
Not something you'll be able to emulate in the small space of a wine refrigerator. The pan would be a more practical improvement.
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