Can CBus talk to the outside world via a serial port?
If so you could get a CM12U (http://www.letsautomate.com/10075.cfm) and maybe communicate with the powerline that way?
However, I'm only guessing the CM12 would respond to commands sent direct to a serial port (rather than through the ActiveHome s/w) but haven't tried this myself.
HTH somewhat
Tim.