Someone Else Posted: Just my opinion but, that would be a TOTAL waste of time! The rail size on 3-rail track systems is historically WAY TOO LARGE for 2-Rail SCALE modeling. Much better to purchase properly sized 2-Rail track & turnouts, with proper sized ties. Then there is always the option of hand-laid track on individual wood ties.
What might be a waste of time to some, is quite possibly an enjoyable modeling experience to others. And who knows? 3-rail, over-sized track with the center rail yanked may be just the 'look' a person could be envisioning. Or perhaps, what if someone wanted to model outside 3rd rail using 3-rail trains? That would be a great way to re-use the left-over middle rail!
All kinds of possibilities open up when one unlocks a closed mind. Just my opinion too, of course.
Just an FYI, in case no one has ever noticed, GarGraves offers 2-rail (yes, two!) O-gauge flex track with either tinplate or stainless steel rails. Shown on their website.