Simple:
Do that.
Custom size reading the file.
Preview how it looks in the crop filters.
My settings are NTSC. Set 339x460 on 352x480 canvas
Adjust for PAL accordingly. Set 339x552 on 352x576 canvas
The same techique applies to converting downloads to DVD:
This is essentially how you restore overscan (tv safe area). Most download sets absolutely SUCK because it has far too much image cropped off (7-10% more than what it should be). The overscan is almost ALWAYS removed by the uploaders, so the downloaders, should it need to be put onto DVD, must correct for overscan on the tv.
FYI, this is NOT an approval of download conversions. They tend to have LOTS of other issues too. This is merely one of them.