Thanks MK_1, this shader from the wiki works:
Code:

material right_alpha_mat
{
  effect =
  "
    technique right_alpha1
    {
      pass p0 {zWriteEnable=true; alphaTestEnable=true;}
    }
  ";
}

action right_alpha_acc
{
  my.material = right_alpha_mat;
  my.dynamic = off;
}


The edges are a bit rough, but the sorting problems are gone without needing to redo the UVs and textures.

Pachinko a Go Go! Super Excite!