We recommend that you install and use the experimental version of APT to get these features. This can be accomplished by adding the experimental archive to your /etc/apt/sources.list:
deb http://ftp.debian.org/debian experimental main
Then you can install the experimental version with apt-get install apt/experimental. We hope to provide backports for stable at some point.
Since this will replace your current APT packages, you may want to keep the older packages around.
If you're just interested in the original patch, you can download it here.