There are two ways to add a single attendee without uploading them to a roster:
Login to SAFe Studio
Click Teach & Manage > Course Administration from the top of the navigational bar
From the My Courses, subtab page select the dropdown arrow to the right of the title underneath Actions
Click Add Attendee and fill in all of the information
You can also do this from inside the class by clicking on the title of the class and using the + Attendee button at the top of that page