I guess that I was wrong in thinking that was what I was looking for in an ad-hoc backup.
I would like to be able to plug in an external hard drive that I want to image and image it without having to change my scheduled backup configuration. Doing the Stand Alone backup requires that the configuration to be completed already. In this case it does not do what I would like.
Each time I want to backup an external drive I need to go through the process of recreating my backup configuration in which it then goes against my computer as a new scheduled backup. When the backup is completed on the external drive I then have to go back and reconfigure my computer's backup schedule to backup my C drive.
A one time backup would be great to be able to use.