Is there a way to create 2-color and 3-color conditional formats in PHPExcel?

Question

I am trying to apply conditional 2-color scale and 3-color scale formats to an Excel worksheet that I create using PHPExcel. Looking at the documentation, it looks like PHPExcel does not support these types of formats (only the "classic" ones).

Without expecting an improvement for PHPExcel, does anyone know how I could implement these types of gradient formats? I don’t think there is any API for adding "raw" Excel XML or something like that?

Or maybe other ideas?

Thanks!