Hm I don't understand two things, your approach from a few years ago (but not that important when it does not work) and more important why the technique would not help in your case? I'm pretty certain that it would.
You render all the vegetation with solid faces, thus there cannot be any sorting errors. Then in a postprocessing step you add the vegetation to your game world and smoothen the edges by alpha blending using one or two alpha masks.
If it should for some reason look poorly close up you can still use regular alpha blending/ rendering for nearby models and use said technique for all other vegetation.