This question presupposes that “de novo” excludes “part of a design.” That seems obviously wrong to me. If that is the question you meant to ask, then it can’t be answered without accepting its nonsensical premise.
It seems to me that you are proposing some kind of magic, and that’s not worth discussing. If instead you are proposing what biologists call “preadaptation,” then we can discuss what that might mean for evolution and/or for whatever it is you mean when you say “a design.” If you are curious about how selection can act “in advance” to “encourage” the development of new coding sequences, see the two papers I mentioned earlier in the thread, especially the one from the Masel group.