Mr. Tee thanks for the request. We will see how the general interest is for this, but in the mean-time please see if this helps you:
You can exit full screen mode (the black button on the top right) and this will bring back the standard excel ribbon bar, from here you can add freeze pane from the VIEW section of the ribbon bar.
Alternatively, you can turn ON the "Click Layout Assist" feature, and you can hide columns or put them into bookmark view by clicking on the header descriptions, so that they dont take up so much of the screen.
Have you tried that feature?