I don't really like the idea of compiling and keeping shaders in the global scope.
They are created whenever the module is imported (which in most cases occurs when Blender is opened) and will rarely be used.
Could you do this in the register function?
In this case however I think it would be best to use the builtin shaders.
If the problem are the matrices, you can use the gpu.matrix module.

with gpu.matrix.push_pop():
    mat = Matrix.Identity(4)
    gpu.matrix.load_matrix(mat)
    gpu.matrix.load_projection_matrix(mat)
    """draw things"""

This module is only loaded when it is actually needed. So compiling the shader at module level is fine.

Yes, took me a while to figure out that I could use the gpu.matrix module... First I tried to set the matrix using uniform_float.
I did not use the builtin shader yet because I liked that I could just offset the vertices in the shader. However I just noticed that I could just use a matrix to move the uv coordinates to the right place. ^^