Isn't this something that you could put in your pixel shader? glPolygonOffset is deprecated now anyway, unless I'm misunderstanding what this "depth bias" function in directx does. Sounds like you could implement whatever you want in the pixel shader.
Where does it say that glPolygonOffset is deprecated?
In a pixel shader? Nope, you can't duplicate what glPolygonOffset. Read the description at http://www.opengl.org/sdk/docs/man3/