How to use 32 bit Integers for Element Indices in WebGL 1.0?
Enabling the extension is as simple as:

var uints_for_indices = gl.getExtension("OES_element_index_uint");


if uints_for_indices is null then the extension is not available and you'll have to split your data anyway.

If it's not null then you can now pass gl.UNSIGNED_INT for the index type into gl.drawElements.