i think we might want to take a second, step back and try to figure out what you want. generally if you are trying to improve rankings and traffic, link development and not robots.txt is the way to go. also make sure you pages have sufficent unique content.
you mentioned you are doing this because of rankings and traffic. why do you think robots.txt will help you? is it because they are just duplicates? also why dont you want google to index the pages it labeled as supplemental?
Hi I want to remove those pages from the index becuase they have little or no content (empty customer reviews etc).
I know it may hurt my page rank on some pages becuase the "real" pages will loose internal link "votes" in google's eyes. But it will atleast cleanup my site index. Based on other threads, it is probably true that Google is penalizing sites becuase of emptpy pages and what not.
If you have empty pages and these pages will never gain good content, then it is wise to get rid of these pages.
If you use robots.txt for this you may lose some link popularity. If you use htaccess to do some 301 redirects you can save the link popularity. For me it would depend on how many pages and how many links from other sites are pointing to these pages.