Try alpha test, you shouldn't need any blending at all.
Yeah, i'm doing this. It seems the implementation in three.js is quirky. It only renders certain faces behind the transparency, and for the rest, there is a hole. I suppose it has to do with face ordering. It probably doesn't work when it's drawing the faces with transparent fragments last. I'll try to dig in the source, but this might be too hard for me.
cmp, my 3d knowledge is a bit rusty, but am I right that face ordering shouldn't really matter? I mean, you get all the fragments in the shader and usually, you would dismiss those with a higher z value, but if there is transparency on, you dismiss this one instead and take the one behind it, right?