Opaque box for Subtitles

I use subtitles for most of my movies/shows and they are much easier to read when there is an opaque box behind them, rather then just a thin border. Having this option would be great. It would be even better if there was an option that lets you change the transparency level of the box.

Examples of what I mean:



This is a small option, but would be a great benefit in XBMC, for us subtitle users