How to Bind 3rd (hidden) uv channel in shader?

its possible to assign uv-coords to a 3rd uv-channel (not in the docs) like so:

var uv1: Vector2[] = new Vector2[4];
uv1[0] = new Vector2(0, 0);
uv1[1] = new Vector2(1, 0);
mesh.uv1 = uv1;

but how can i Bind that in my shader? currently i bind like this:

BindChannels {
   Bind "Vertex", vertex
   Bind "texcoord", texcoord0
   Bind "texcoord1", texcoord1
   -- how to bind these 3rd coords here? --

or do you know any other trick to get more than 2 uv channels to work?

If you’re going to use a fixed function shader, you may be able to get it to work by taking manual control of rendering. But it would be a big pain; you’d need to render, then update the UVs, then render again. Unity is not set up to deal with that gracefully. Avoid that, if you can stuff the other UVs into some other attribute (normal, tangent, uv1, uv2, color). You’ll have to write a programmable shader for that, though.