Side-note: I have a similar "run as this other (non-root) user" case which is solved very nicely with sudo - anyone can run the script, but if the script detects it's run by the wrong user, it sudo's itself. And then I can give everyone appropriate access to run it with or without a password as required.

Besides, I'm not entirely clear on why writing via a symlink is a bad idea. Generally speaking, it's a very good idea to ignore the fact that a file is really a symlink to somewhere else. Lots of really cool unixy things happen when you don't worry about symlinks. You may have a special case, but the chances of that is low - that's why it's a special case. ;-)