Well, I only fertilize neps now. I have fertilized helis and cephs in the past, and it didn't seem to really hurt them, but I find it difficult to gauge what they like or don't like, so I just keep it in the pitchers. Plus, it's less maintenance when you don't allow the media to break down as quickly. I would buy some decent fish food to put in the pitchers and maybe use a pipette to add liquid fertilizer to them as well. You can experiment with root fertilization, but it can cause some problems if the media isn't loose enough. And when I say "feed," I usually mean adding nutrients to the pitchers - although it's really the same thing either way.
Unless it gets too hot, you might consider putting the plants closer to the lights. I keep my small Nepenthes roughly 18'' away from the lights, while some of my larger plants are growing within a few inches of them. Helis and Cephs could probably be within a foot of the lights, with perhaps a bit of mist blowing on them to keep them cool. There's a huge difference in PAR between 24'' and 18'', let alone 18'' and <12'', and the plants will definitely utilize it if the leaf temp. doesn't become too high (although you can offset this with high CO2).