There is no camera solution for this on sketchfab. It is tricky anyway because currently the rotation is limited to 90 / -90 deg if it were to go beyond this then at the point it gets to 90 deg the camera actually has to do a 180 deg rotation on its forward axis or else you would sit with the exact same problem … the camera would be upside down, this would suite your need , but for the most part would be weird looking on most other models
Anyway it is not possible, what you need to do to solve this is actually animate the object, then users can select a animation to view the object on both side properly. Not the best solution but sadly the only option you have.
EDIT, I guess you can rotate the object by 90 deg on the x axis , then looking from the top down and the bottom up would give you the views you need to see the correct orientation of the text.