Hmmm, they don't work for me either. I also tried to put an offset on one of the hardware sensors, and that worked. But not the software ones.
For a work-around I was going to try setting up a virtual sensor to use only one software sensor and see if I could apply an offset to the virtual sensor, but they don't have offsets. Looks like offsets have to be applied in the settings for the actual sensors themselves.
Pooey