Here are the commands I could find. I don't think any of them do that.
Usage: SubtitleEdit /convert <pattern> <name-of-format-without-spaces> [<optional-parameters>]
one or more file name patterns separated by commas
relative patterns are relative to /inputfolder if specified
/track-number:<comma separated track number list>
/multiplereplace:<comma separated file name list> ('.' represents the default replace rules)
/multiplereplace (equivalent to /multiplereplace:.)
/ocrengine:<ocr engine> ("tesseract"/"nOCR")
The following operations are applied in command line order
from left to right, and can be specified multiple times.
Example: SubtitleEdit /convert *.srt sami
Show this usage message: SubtitleEdit /help
List available formats: SubtitleEdit /help formats
Regardless, I've since solved the problem by creating a second but private share that points to the same location. So I can still have the read only one for guest access, but the other requires credentials. Didn't know I could do that before.