There is a simple, pro solution to this and it is have a framebuilder make you a seatpost that can do this.
A simple iteration would be a bunch of segments of chromoly tubes, which may need the part that goes in the frame to be turned, and then have the last segment be a 22.2mm one such that it can take a cheap saddle clamp. A more sophisticated version could have guts transplanted from another seatpost.
There is an open question with all of this whether your frame can handle this kind of leverage at the seatpost opening without flaring open. My guess is probably not, and there's no way to solve that problem. There are bikes that are designed to have much more setback than others, i.e. most Electras and their many copies, so you are not playing in a new sandbox here, but those frames have slacker seattubes to keep the aforementioned leverage down.