Why not leave the pipes with the sensor bosses and sensors in place? Replace the cats with "test pipes".
EGO sensors have a good deal to say about the fuel/air mixture ratio. If you remove the rear sensors, the system should detect the absence of the sensors as a malfunction and go into a limp-home mode that may or may not adversely affect performance and/or fuel mileage.
I really don't see the logic behind removing the cat converters. They have very little flow resistance and don't cut down performance in any real way.....maybe a couple of percent that would only be important if you were running at the speedway in Daytona.