I have tried the 2/3 method, it even become more painful(you can try at a piano).
You can break this movement down
How to exactly drill the motion would require that I sit besides you and see how you are doing it. But here is some general advice.
This would make a great pairing with Totentanz, but those tremolos are keeping me from getting started! They're just not happening with me.
I reckon that if you don't have a very comfortable span of a tenth, this piece just isn't worth the bother. There are lots of other fun transcriptions to work on without killing yourself. It's a good piece, just not written for smaller hands, end of subject.