import os

def generate_cad_model(dimensions):
    """
    Placeholder for generating CAD models.
    If FreeCAD is unavailable, return a pre-generated example CAD file.
    """
    length, width, height = map(float, dimensions.split('x'))
    # Mock result for environments without FreeCAD
    example_cad_path = "/mnt/data/example_model.step"
    if not os.path.exists(example_cad_path):
        with open(example_cad_path, 'w') as f:
            f.write("Example CAD model for dimensions: {}x{}x{}".format(length, width, height))
    return example_cad_path