I was asked to bring in a teleprompter for a major brokerage firm in San Francisco. It was the 40th anniversary of their founding so they were making a big deal of the production, using RED cameras paired with big lenses. On top of that, they requested the ability to prompt at 90º since their camera would be tilted on its side to enable vertical 9:16 when presented.
The solution was to mount the prompter freestanding on our C-stand, so that the camera could be angled however it needed to be on its OWN tripod. This way the text is the correct orientation for the speaker.
If it wasn’t a locked off shot—perhaps a dolly or slider move—there is a bracket that tilts the whole camera and prompter package on their side, together.