That crossed my mind but according to the CSS3 spec the border edges are supposed to be flat, and not diagonal (which is what makes this hack so efficient). Thi

That crossed my mind but according to the CSS3 spec the border edges are supposed to be flat, and not diagonal (which is what makes this hack so efficient). This could end up being implementation-specific but ATM probably wouldn't provide the solution (it also doesn't yield a way to do perspective transforms on an image).