I was hesitant to answer, because I'm not really an expert, but here goes. I think that, while they definitely can produce roots from the stem, they usually don't. Unlike plants such as tomatoes, which produce copious root nodes from any part of the stem that senses moisture or darkness, Nepenthes mostly grow new roots from tissue underneath the outer "bark" layer. (I've also been told that the side nodes just above each leaf can turn into roots, but I haven't seen a lot of research or anecdotal evidence to support that.) So, I imagine that growing new roots spontaneously is pretty rare. Many growers recommend shaving the outer layer off, or cutting shallow, vertical slits into it, when making cuttings in order to encourage the formation of new roots.
If you want a low-growing plant, it would be a safer bet to take a cutting from the still-green parts of the stem and attempt to root it. If the plant is mature enough, with a little luck the rootstock should produce new basal nodes. Some plants are reluctant to produce basals though, and will resume growing from a node near the cut part of the vine. At the very least, the cutting will remain short for a time.
Another idea, if your vine is long enough, is to allow it to grow hanging over the edge of the pot, so that the tip of the vine is lower than the rootstock. This will trick the plant hormonally into producing new nodes, as if it were cut.
~Joe