One of the keys factors in growing large Cephalotus pitchers seems to be associated with the humidity level surrounding the plant during the growing season. A morning and lunchtime hand misting is a good start, but even better is growing under a bell jar or in a terrarium, as long as they are not in full sun where the temperature could rise to extremes.
A level of around 70% humidity seems to be ideal and if this can be coupled with some movement of the air, by using a fan, so much the better.
In my greenhouse I've been using an ultrasonic humidifier that produces a constant stream of cool mist/fog, this I have combined with a timer that is set to come on around dawn for an hour and again early to mid afternoon for 2 hours. The humidifier is controlled by a humidistat that switches itself off when the humidity reaches 80% and back on again when it drops to around 60%. This is ideal in the summer because when the temperature rises during the day the humidity drops, but, during the summer nights the humidity rises naturally because of the temperature drop.
I disconnect the humidifier during the autumn/winter season from early October to late April as the natural cool weather humidity is sufficient and with the lower light levels too much humidity combined with slower growth can and does encourage Botrytis moulds.