I have created a new QGIS plugin to export CZML files representing billboards / labels.
It is latest version 0.2 is now online in QGIS plugin repository as Experimental plugin.
Basically, you can select any point based vector layer in your GIS dataset and specify the CZML with it’s attributes; then export it.
Please feel free to contact, give feedback or any suggestions for it.
Plugin in QGIS repository: