>>2629178You're going to need Photoshop CS. As you know, using the clone tool is a huge hassle. I don't think Lightroom was even meant for something like what you've got.
Any way:
>Select all the buildings, using either the rectangular selection tool or the lasso tool>Invert selection>Filter > noise > dust and scratches>Radius 1, Threshold 0>Enter, doneYou don't even need to burden yourself with the task of perfectly tracing each building; just get the general shape of the buildings and you should be good here.