Subtitle margin width problem

[buggaboo]

Hi. I'm using the TV-out feature of my video card to watch movies with my TV. I set a negative custom pan-scan so I can fit the video correctly in the TV screen. This works fine, except for subtitles, which are cut in both sides and the subtitle margin width option doesn't seem to work.

Is there a way to make the subtitles fit according to the video window width? I mean, so that the subtitles width is aligned with the video width, like in the attached picture.

Thanks.