Below is a castle I modeled ‘loosely’ based around the Cinderella Castle. If you look at the windows, it doesn’t have any reflection on it because there is nothing in the scene to reflect.
To make it have reflection without creating any more objects in the scene, I went to the Hypershade window and created a EnvSphere. You can find this in the left sidebar under Create Maya Nodes -> Env Textures -> EnvSphere. Middle-mouse-drag this to the Work Space.
I clicked on the new EnvSphere node and opened up the Attribute editor. Under Environment Sphere Attributes, I clicked on the Image box and connected A 2D texture file as projection.
In its Projection Attributes, I set the projection type to be planar and connected an image file; an image of what I wanted the windows to reflect.
The EnvSphere node was now set up. This EnvSphere was then connected to the Reflection Color of the window material. To do so, I middle-mouse-dragged the EnvSphere in the Hypershade window to the window material’s Reflection Color slot in the Attributes window.
To make the reflection map appear in the windows, I clicked on the new place3DTexture1 (which was created when I set up the EnvSphere node) in Outliner. Under 3D Texture Placement Attributes, I clicked on Fit to Group BB Box.
This resized and moved the projection plane like below.
After some manual resizing and tralslation of the projection plane, the windows were using the reflection map as desired.
And below is a 12 second video of the Cinderella Castle.