I don't think such thing can technically exists.
Just keep in mind it took *years* for Adobe to port Photoshop to 64 bit, and that's a program that generates way more revenues than FSX ever did, so they had most of their resources on it. FSX is task comparable in complexity, in fact it also has started an industry in add-ons, just like Photoshop, that will all need to be ported to 64 bit too, just like Photoshop.
I think that if I made a program that would tweak the frame rate *counter* to show higher numbers, many people will be convinced their sim IS running more smoothly. But I would never think about selling it...