EnOcean's website is very informative, concerning battery-less technology. I will be reading through their white papers on the topic for future use!
@RalfB, do you have specs for the switch you want to interface? littleBits uses 3 wires, a +5 volt, a ground and an analog signal that varies between ground and +5 volts. If the EnOcean switch can mate to that directly, it should be easy. If not, there may be some more work involved.