Well, I too have succumbed to the lure of java for my Nepenthes -- this after talking to a number of people whom I respect, both on this forum, and some others who have also sworn by it. Like those before me, I have simply poured cool coffee (made with RO water) through the media, as I would a conventional watering. I did, however, dilute the coffee a bit, simply because my tastes run toward the pitch black with roughly the texture of gelatin.
In recent years, I have had the "fortunate" though time-consuming opportunity of germinating Nepenthes from seed, and have also fed half of those most recent plants with the coffee; the balance will remain untreated, save for a standard biweekly application of 30:10:10 orchid fertilizer (which they've been given since sprouting), which the coffee-fed will also receive.
A few of my older plants were also "dosed" on 13 March, along with the others, which I'll update six to eight weeks from now:
Nepenthes villosa -- March 2010