I saw this artwork for Daft Punk's "Get Lucky" song and it begged the question "How was that shot?"
My guess is an extreme telephoto lens allowing the sun and the band to be visually compressed together.
How is this effect achieved?
The composition is easy: a long telephoto lens in the 1000mm-1500mm range (full-frame equivalent) will have the sun just about completely fill the image.
Composing safely is another matter entirely. That low on the horizon, the sun is safe to look at directly, but looking at it through such a strong telephoto lens might not be. I'm guessing the photographer framed the shot ahead of time, made a good guess at the exposure, and took a blind shot when the sun looked to be in about the right place.
I think you already answered your own question, well pretty much. I never tried your guess, but theoretically makes sense to me.
If are not a purist, you can take two photos and merge them on Photoshop. So first take a picture of the sunset you need, then take a photo of your subject's silhouette (using a bright bac, overlap and resize both images on Photoshop so they look natural.