Operation of two 3-way occupancy switches
The occupancy sensors that are commercially available, are not designed to work in this situation. 

You could install the sensor in a location that covers both the door, and the rest of the basement.  This way the sensor would "see" you the whole time you're in the basement.

The other option is to roll your own solution, which would likely include multiple sensors and some form of central processor. Maybe some motion sensors and an arduino or raspberry pi.