I've been squirting Maxsea into my small Nepenthes pitchers, though it hasn't been long enough to know how much it helps.
In addition to all of the above suggestions, there was a great article by veteran grower, Bob Sacilotto, in a 2004 CPN newsletter: CPN Samples
He went through great lengths to feed seedling Nepenthes, including the application of fertilizer into juvenile pitchers, using, of all things, hollow deer hair as a pipette. It is a scholarly article, which has helped me, over the years, both in growing highlanders -- and, indirectly, even with their micropropagation . . .
“Sì perché l'autorità dell'opinione di mille nelle scienze non val per una scintilla di ragione di un solo . . ."
-- Galileo "Biff" Galilei
Nice article, but after reading it I want an Edwardsiana (curse my plant addiction). It should help with my ventricosa though, thanks.
You'd probably also be surprised at how much they can catch on their own. Even if they're in an enclosed environment. I'm consistently amazed at how many small gnats and midge like flys my small seedlings have caught when ever I peak into their pitchers. It seems my grow chamber has a sustainable population of them. Even the tiniest of newly formed pitchers even catch them, the pitchers are so small and thin you can see the shadows of its prey through the pitcher. But despite them catching their own food I still very much enjoy feeding them, after all thats what makes growing Cps so fun. At least for me.