Could you give more information - "the package guidelines suggest that binaries should go into /opt" ?
I think that the Debian and the Debian based don't use the /opt directory. By the LinuxFilesystemTreeOverview /1/:
"/opt can be used to store addition software for your system, which is not handled by the package manager."
If you want to use the /opt, you could make the symlinks /2/, /3/, /4/ to the /usr/bin etc.
The Project Neon /5/ is packaging the development versions of the Amarok and the KDE to /opt so they can be used side by side the stable versions.
The Neon has a ppa /6/ so you could donwload the source packages and examine them.
Thoughts after reading the http://developer.ubuntu.com/publish/my-apps-packages/.
"Be able to be installed into /opt/"
just means that the source should run from the /opt/. It does not be in the $PATH, if you are calling it with the full path.
Here the development version of the Amarok is installed under the /opt and the Exec /1/,/2/ key is:
But this is only my impression !