Your train picture isn't something that would be a candidate for this technique, but a brick building or something with a consistent background. You have to smudge your object you wish removed, from outside the object edge inward, then when you are happy with the colors layer, switch to grain merge layer and use the clone tool to clean up.
Done in a hurry, so I wasn't trying very hard to do this:
Run Leon's script:
Example image...

Switch to colors layer, and using smudge tool, smudge the object to be removed using outside to inside strokes. You only want to smudge the object, NOT around the outside of the object.
Once it leaves a grain contrast look, then switch to the grain layer and use the clone tool to begin cleaning up the contrast areas.
Switch back to the colors layer and smudge the remaining artifacts until you are happy.
My quick end result:

I actually over-smudged it, but I wasn't trying to be a perfectionist. The potential for this script is when your background is something with a consistent pattern.
I had to throw this in there. I used Resynthesizer and saved 5 minutes:

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"In order to attain the impossible, one must attempt the absurd."
~ Miguel de Cervantes