I think your plea is too late. My understanding is that it is impossible to add IBIS. Fuji made compromises to make the body and lenses the size they are, and this is one of them. This, combined with corner sharpness concerns, has led to a choice that may or may not get you where you want to go. If it helps any, I know IBIS becomes less effective the longer the lens.
I totally understand preferring Fuji over Sony. I personally loathe the UI/UX of Sony cameras. It's like shooting photos using a Playstation. That said, if I was shooting professionally and I had to have a long fast prime with OIS, I would go with a company that gave me that option. When it's paying the bills, sometimes you've gotta make hard decisions about what camera can really do the job. I sort of doubt anyone will criticize you!
My guess is that long term, Fuji will unveil a prime in this focal length / f stop with OIS, which would be just as good. Until then, You might be on the wrong system... Sorry friend!