In response to the "New Idea: Steam Nicknames!" thread, I decided I'd take it upon myself to develop a program capable of actually doing what the OP was looking for.
Here's a quick video to show it in action: http://screencast.com/t/pVGdyX2a
You might be wondering how this is possible. The answer is very simple: Valve already implemented nicknames or "aliases" for friends. All the functionality exists, but there is no way to access it within Steam. This is why I made this quick tool.
You can download the latest versions here: https://bitbucket.org/VoiDeD/open-steamworks/downloads
As always, with most software, there are bound to be bugs and other various issues. Make sure to let me know of any issues you encounter, and any suggestions are welcome too.
Also, the source code is available for public viewing here: https://bitbucket.org/VoiDeD/open-st...FriendManager/