Shoot the upcoming eclipse

Years ago I got some images of the moon that were semi-descent using a 300mm lens.
I want to shoot the upcoming eclipse but...this time I want to fill the frame with the moon.

Set up a reflected moon in a mirror and use a macro lens to capture that image.
Would not getting close to that mirror, using a macro lens, be more able to fill that frame on my dated 1Ds3.

Is this a viable method...or another one of my dumb ideas?

My mind is waffling back and forth between the physics of this being idiotic and genius. You know how you hear it said, "That's just crazy enough to work." This one might need just a little bit more crazy. Either way I'm in to see what the actual knowledgeable people say.

I'm hoping the latter...but will accept the former as a humbling experience

If it works what you'll have is an image of the moon that fills the frame, but it will only have as much detail as the reflected image -it's not like you're gonna capture any additional detail just because you're using a macro lens. The tricky part will be focusing on an incline -not gonna be able to get the plane of focus flat with the mirror unless you have a tilt shift macro lens. So if it works you're looking at focus stacking a moving subject with a long focal length macro lens (so you have enough room between the lens and the mirror). IMHO you're better off just adding a 1.4x teleconverter to that 300mm lens and using a 1.6x crop sensor camera...

I know the eclipse is over, but I thought this sounded like an interesting experiment. I tried shooting the bathroom door in the mirror and focused at 1:1 all I got was dust specs and a blurry door/wall. I focused until the door was in focus and it just looked like I shot the picture from 3ft away.

Then I remembered that when shooting in mirrors, you still have to take the distance of the object being reflected into account. Say your camera is 2ft from the mirror and the subject is 8ft away from the mirror. Your lens will be focused at 10ft. So sadly, no it wont work.