non-blocking SwapBuffers() with VSync=on

Question

I am looking for a portable way to make a non-blocking SwapBuffers() even if VSync is activated.
In other words, is it possible to to be notified by an event or to know the delay until the next VSync ?

Answer 1

IIRC this extension helps: http://www.opengl.org/registry/specs/SGI/video_sync.txt, but it is very poorly supported with current drivers.