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You could convert a stock XLR. You'd need to reduce the travel - easy with plastic spacers - and reduce the air chamber volume to keep the spring rate sensible. Not quite so easy, but you can do it brute force simply buy pooring a volume of suspension fluid into the air chamber.
Just means you carrying round an extra amount of plastic, fluid and damper shaft that you don't really need.
All [most] lefties are effectively designed for 26" wheels, then reduced to fit their application. Oliver might be different, or it might just be a carbon with a load of spacers in it. Who knows.
You suggested that you could modify an existing Lefty fairly easily?