I've read about 2 methods people use to clean their o2 sensors. I have no Idea if this would work for a wideband sensor or not, I've only tried it on a narrowband sensor.
One says to leave the end soaking in gasoline or seafoam overnight, and clean it out with a brush.
The other method is to heat the end with a propane torch til it's glowing, then dunk it in water.
I actually tried the heating/water one today (narrowband), and black gunk seemed to jump out of the sensor, it was kind of cool. I've yet to run the car with it though, (my wife's 240sx)
I'll let you know how it turns out.