Possible to emulate GL_EXT_texture_rg + (GL_OES_texture_float|GL_OES_texture_half_float)?

Hello.

I'm implementing a renderer that uses variance shadow maps. I've
implemented the technique on OpenGL >= 3.0 core contexts, and on ES3
with GL_EXT_color_buffer_float and GL_EXT_color_buffer_half_float.
However, I'd also like to implement it on ES2, and for that I'd like to
get access to context that exposes exactly those extensions given in the
subject (so that I can test that all the various texture
parameters are correct).

Unfortunately, even though the ES3 context exposes
GL_EXT_color_buffer_float and GL_EXT_texture_rg, it doesn't expose
GL_OES_texture_float (which, if I follow the specifications to the
letter, means that I don't get colour-renderable floating point textures
on ES2). The ES3 context (when being treated as an ES2 context) seems
to agree:

Mesa: User error: GL_INVALID_OPERATION in glTexImage2D(format = GL_RED,
type = GL_FLOAT, internalFormat = GL_RED)

According to:

  https://www.khronos.org/registry/gles/extensions/EXT/EXT_texture_rg.txt

The call is valid iff GL_EXT_texture_rg and GL_OES_texture_float are
present.

Is it possible to get mesa to emulate these calls? Or will I need to
patch the source?

M