If you mean by "without cancelling" without substituting it in the video-file itself:
Yes .... Some skins will provide a direct link for that.
Otherwise:
rightclick > Load external audiofile (etc)
or
Shift+L
(Videofile should be loaded to use this).
If you mean by "without cancelling" without suppressing main audio during playback:
No, not in a straightforward way at present in as far as I am aware of, but maybe there's a WinAmp2 DSP to do that trick (havn't searched for it yet!)