Without shaders (normals, etc) you're best bet will be to make the texture as good as possible, painting in highlights and such since you can't simulate it otherwise.

For example:
https://2.bp.blogspot.com/_ssBv_CErlq...oly-altair.jpg

This model of the character from Assassin's Creed is less then 700 polys, yet looks very good for that poly range.

When you are that limited with polygons and have no fancy shaders, it all really comes down to the quality of the texture.