The perils of lurking on a site...my post count is not high enough to be able to reply to messages or post links.
The brackets for the solo seat set-up assume that the passenger grab rails are removed, and mount to the frame using the same location that the rails would mount to. If the rails are present, the brackets for the dual-seat set-up is designed instead to mount to the rails. So, it's really more a question of whether the rails are installed or removed that play into which brackets work, and not so much whether the passenger seat is removed or not.
I have no personal experience with the Corbin dual seat, but found another thread that indicates that the brackets and stays work without issue. I'm not able to post a link, so search for the thread titled "saddlebags, bar risers, and Corbin seat?" for more detail.
I am willing to break up the stays and the brackets, if someone would like to buy one without the other.
Since I can not reply via messaging, please email seajay7993 (at) outlook (dot) com.