I'd put fake paper namers (doi.numbers.whatever.zip) in order to quickly keep their attention, among a robots.txt file for a /papers subdirectory to 'disallow'

I'd put fake paper namers (doi.numbers.whatever.zip) in order to quickly keep their attention, among a robots.txt file for a /papers subdirectory to 'disallow' it. Add some index.html with links to fake 'papers' and in a week these crawlers will blacklist your like crazy.