That's the problem with CDG. Most of the time you're stuck with the premade. I haven't have the change to try the transparency to see how well it work with the text.
Anyway, I've written a software that will take a mp3 files along with the lyric file and it'll superimpose the word over the video on the fly. You can even use live video.
I'll look supporting CDG in the future if there's enough interest in it.
You can download at
http://www.walasoft.com/walaoke