The real solution is to get a secondary processor that can handle these transitions well.
The OSSC handles these transitions as fast as anything on the market as far as I’m aware. The only way to do it would be some kind of framerate unlocked device with a frame buffer, maybe that’s XPC-4? I seem to remember someone said one of the cheaper scalers does it by basically outputting everything at 59.94 and framerate converting all input. Of course that then causes scroll stutter.