Your ortho camera handles the viewing frustum. Everything in the frustum will be projected to the viewport. What you are wanting to do is keep the frustum at a constant size, and change the size of the viewport (which is the correct way to do this).

So, just make your viewport represent the size of your screen, and OpenGL ES will stretch the frustum however it needs to.

On the note of duplicate art though, you really should try to provide one for each density; ldpi, mdpi, hdpi. Otherwise your game may look excessively stretched or shrunk. The extra assets can diminish this effect a bit.

Your ortho camera handles the viewing frustum. Everything in the frustum will be projected to the viewport. What you are wanting to do is keep the frustum at a constant size, and change the size of the viewport (which is the correct way to do this).

[edit: The frustum is a 3D representation of space that defines the visible portion of your scene. Effectively a large rectangular prism, things inside get projected to the viewport, things outside do not.]

So, just make your viewport represent the size of your screen, and OpenGL ES will stretch the frustum however it needs to. Define all of your screen elements relative to the inside of the frustum.

On the note of duplicate art though, you really should try to provide one for each density; ldpi, mdpi, hdpi. Otherwise your game may look excessively stretched or shrunk. The extra assets can diminish this effect a bit.