I haven't tried the coffee method, but one thing to keep in mind. I would never, ever pour coffee onto my plants without first looking over my coffee pot and cleaning it extremely thoroughly. I have taken mine apart already and the tubes that the water goes through were almost caked shut with mineral deposits. They sell brushes and solution to clean this. If you don't, Your asking for trouble. Reverse Osmosis water or not, you'll be adding minerals to your coffee and killing your plants. Like watering them with regular tap water, or worse.
Mineral-laden water doesn't seem to have the same deleterious effect on Nepenthes (I've tested tap water upwards of 350-400 ppm on my plants without a problem) than would otherwise be the case with most other carnivorous genera; and, besides, a biannual coffee application should hardly pose a threat, considering how often they are watered and -- typically -- how well-drained the compost.
Anyway, I generally use a French press or stove-top espresso maker; no Mister Coffee . . .
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