No it would require an editor instead of a player.
But I wonder why you would want it (unless you would prefer another player which has no provision for showing subtitles like BSPlayer)?
If you name the subtitle-file the same as the avi (except for the extension of course) and put both in the same (directory)map or on the same CD, the subtitles will start automatically in BSPlayer (unless - of course- you have opted this automatically playing out in BSPlayer's Options/Preferences/Subtitles)
