However, a quick scan of a file or two in /usr/share/apps/libkholidays/plan2 would tell you that the syntax is not at all rocket science. You could then customise one to your needs and put it in ~/.kde4/share/apps/libkholidays/plan2 (make the directories if not already there). I've pushed holidays for Singapore upstream awaiting approval.
Still, this is a very roundabout way of doing something that should've been made a no-brainer by now. Parsing at least XML is a way better approach, if not iCal. I hear the situation with Evolution is not any better, since you'd have to first add a public calender to your Google Calender, and then sync Evolution to that calender.