If you need to back up every design decision that you make with a relevant usability study or research paper, you won't be able to get much done.
If you've worn out Jacob Nielson, you could try Johan Petersson
http://www.trilithium.com/johan/2005/03/target-blank/
When dealing with your type of audience who just don't get it, the following has some good points: http://000fff.org/design-discussion-principles-how-to-get-your-client-to-love-your-design/
It's important to look at the goals of your manager or client who wants you to implement the "open in new window" functionality; they are not stupid, they are probably trying to e.g. keep users on the original site - if you gently point out the fact that the new window doesn't have the back button enabled in all(?) browsers such that it prevents users navigating back to your site, they might come around.
If not, and they have greater authority over the design, you'll have to go with their decision - it could be reversed later if you can show a real world example of it leading the user astray, or if your stats show that the user doesn't return after a new-window exit.