Here is an old patch (2008!!!) allowing 2 pass transparency with jit.gl.sketch.
it's based on chapter 10 of openGL
The nice feature is that it's able to render transparency and depth without having to z-sort the objects.
One application for the alpha test is to implement a transparency algorithm. Render your entire scene twice, the first time accepting only fragments with alpha values of one, and the second time accepting fragments with alpha values that aren't equal to one. Turn the depth buffer on during both passes, but disable depth buffer writing during the second pass.
Structuring the sketch commands is a bit complicate, so :
Do you think this technique could be implemented with jit.gl.node and 2 capturing cameras for examples. mixing them after...
or with shaders aplied to cameras...