This Strong™ Coupler is an excellent solution to join two pipes together and has an open face to offer an access point to the extension pole.
Strong™ Open Face Female-to-Female Coupler for Ceiling Mounts
This Strong™ Coupler is an excellent solution to join two pipes together and has an open face to offer an access point to the extension pole.
Universal Fit
With 11.5 threads per inch, this suspended ceiling adapter will work with any poles using 1.5" NPS schedule 40 interface.
Open Faced
Utilizing a 1.5" x 1.5" hole, you can easily feed wires into this connection point between the two pipes. 
Locking
Includes set screws to lock down the pipe's rotation so you can set it and forget it.