Indeed you can use a Generic Serial Device to implement the serial interface for UPB (as any serial device) using ruby scripting language.
But our lighting support (X10, Z-Wave) is using some special devices, not GSD based. There is no way to use it for UPB.
Please fill a mantis report so that we will try to analize the protocol. Well, if you have some ruby knowledges, you can try to implement at least some basic commands.