@JoshMohrJust an FYI...you can actually accomplish this, just not thru the Flow editor. It would be a lot easier thru the editor, but you can make output fields non-required with the following steps:
Export your Flow
Edit the 'Definition.json' in the export package to remove the output fields you don't need from the "required" property of the 'For a selected item' trigger
Re-import the Flow package
This makes the fields optional when the end user triggers the Flow.
Just be aware that the 'For a selected item' trigger will not pass any fields that were left blank into the Flow. So, your Flow needs to check for the presence of a field in the trigger output before attempting to manipulate the field contents.