Mexican Pinguicula do not have a "dormancy". Dormancy is like hibernation, and is without active growth or development. These plants simply change their leaf form when their environment changes. In cultivation they do not always do this, nor is it essential for their health. A few of these species retreat beneath the soil when they are in their Winter leaf form - most of these prove they aren't "dormant" by flowering from beneath the soil.
For more than four years I grew all of my large variety of Mexican and other tropical Pinguicula continuously floating in trays of water under "cool white" fluorescent lights with varying periods of light and dark. All thrived very well, those that received the highest levels of illumination, duration and intensity, without generating high temperatures, responded best. For various reasons my entire collection has gone without water (other than fluctuating humidity levels) since the late Summer of 2007. I did maintain my usual lighting, and those that have done best have been under illumination continuously during this entire period.
I will soon post a more detailed description, and include photographs.
One environmental factor that I believe to be of importance is the natural intensity of UV light in the regions where these plants originate. In the vicinity of the equator, natural UV intensity is some of the most intense on the planet. Then consider that they often grow at high elevations in this region, which subjects them to even higher levels of UV light than they would experience at lower elevations. One of the few ways to provide high UV levels in cultivation is by use of fluorescent lighting which leaks excess UV while in normal operation.