First merge all the common dimensions in your report.
Now in variable section on right side of report choose new & create new variable "get_site_name" as mentioned above.
after then again choose new variable & create "Final_site_name".
Now go to first tab -> in Analysis section you will have filter there add new filter & choose measure object Final_site_name -> Operator "Not in list" -> write 1 there click on ">" button & choose OK.
Now you will see your desired output.
Sorry I can not present any snapshot here as I don't have WEBI installed on my system currently
Thanks,
Swapnil