Unfortunately for your crusade, the soft-G pronunciation has essentially been typo-squatted since before typo-squatting was a thing.

https://file.org/extension/jif

https://fileinfo.com/extension/jiff

https://www.reddit.com/r/todayilearned/comments/4rirr8/til_t...

https://en.wikipedia.org/wiki/JPEG#JPEG_files