It used to be possible using iMobileCinema, a Safari plugin that directed flash videos to the Quicktime player. I don't think it's been updated in awhile though. You'll have to google for more info.
It is using cydia, called safari download plug in, which allows u to download or stream any megaupload download (which also generally is a megavideo link) but its as if your downloading it anyways i think... not sure if it works, but try it none the less
