The Kantian transform would be to keep the phenomena just the same but change the noumenon. In other words a high-class version of the geek's 'brain upload' idea. It fails because it would mean that you could be duplicated at no cost - phenomena are already virtual - and if that was to occur you and/or your new clones would immediately go to war with each other, or some other high intensity engagement, premised on precisely the zero-sum noumenon, (as in a certain recent novel.*) Hence the plausibility of will as thing-in-itself. And if you can't just change the noumenon? Then phenomenon is not really phenomenon and noumenon not really noumenon. Inseparable they are not-two.
*L'anomalie by H. le Tellier.