During the Randa meeting I implemented some magic in KIconThemes to generalize a design initially made by Christoph Cullmann for Kate.
On platforms other than Linux/BSD, icon themes are not available as part of the system, and installing 6235 files takes forever. The deployment strategy for applications on those operations systems is now the following:
Therefore, no code modification is needed in KDE applications, to make them find an icon theme from a rcc file, it's just a matter of packaging the desired theme into the right location. And the users can even swap that with another theme rcc file easily if they want to.
The official long-term version of this explanation is available in the KIconThemes API documentation.