ShaderMaterial

I'm trying to construct a custom mesh using ShaderMaterial porting some code from three.js.

In the example I'm copying though, since the shape is only 2d, they save performance by making the vertex positions in a vec2 buffer instead of vec3 and they don't use any indices at all (it just uses gl.TRIANGLE calls to make each set of 3 verts into a triangle.

The problem I am having is that if I don't do setVerticesData with the full vec3 vertices and then setIndices with a list of indices, Babylon doesn't seem to draw anything.

Is there some way to do these kind of tricks without having to fill in all the vertices and generate the indices manually?

Thanks!