Standard Shader and Height Map on iOS using OpenGL ES 2.0

I am trying to use the Standard Shader using OpenGL ES 2.0. I don't want to switch to 3.0 because that drops support for older devices (iPhone 4S, iPhone 5, and iPhone 5C). When I run the app on any iPhone using 2.0, the shader works except for the Height Map, meaning the height map does not affect the shader. If I run it on an iPhone using 3.0 the height map works. Is there any way I can keep using the standard shader but get the height map to work on mobile? I am using Unity 5.0.2.