If you've got a link on the page, the PR will flow through it. If you have nofollow, the link juice just disappears and doesn't help anyone.

The same applies if you use any method of robots exclusion. If your aim is to "preserve" pagerank for yourself then you would have to write the link in a way that is unreadable to search engines.

If you're just trying to stop someone getting link benefit, then nofollow, robots exclusion are all possibilities.

nofollow, robots and javascript will block the PR flow

use javascript to write the link.
put the javascript in an external file.
use robots.txt to exclude access to the javascript file.

Out of sheer curiosity, are you trying to do this so the owner of the site the link is pointing to will not know the link doesn't pass weight? IOW does the fact the link does not pass weight need to be generally undetectable?

And, if not, you should be able to run the link through a server-side redirect script and exclude that file in the robots.txt, which is much the same as the suggestion above.

Google can read javascript. use robots.txt and nofollow