Well you could....but it would just sound stupid! I believe Andre Watts does something like that, and it's kind of cool, but it doesn't really work.
Why on earth would you ever want to play the beginning of the toccata, then when it gets to the scherzo use the ossia to build up?? then go back into the second cadenza? The would sound absolutly riddiculous! I mean it would start of as a fast toccata, then change into chords and interlocking octaves at Fortissimo, and then instead of following through, you cut the texture and start scherzoing again, and then play the end of the cadenza, which will of course have no effect becasue you will have climaxed already. Aside from that, you will probably have to change some harmony God knows what else to actually get a smooth transition.
Why do you want to change it? I mean if you do change it, at least be a little more imaginative!