Making such a bbcode is very simple and I could provide all the code necessary to do so as I have it on my own forum, but I doubt admins would grant your wish. Still, here's a working code if you need it.
Code:
BBCode usage :
[soundcloud]{URL}[/soundcloud]
HTML Replacement :
<object height="81" width="100%"><param name="movie" value="http://player.soundcloud.com/player.swf?url={URL}&g=bb"></param><param name="allowscriptaccess" value="always"></param><embed allowscriptaccess="always" height="81" src="http://player.soundcloud.com/player.swf?url={URL}&g=bb" type="application/x-shockwave-flash" width="100%"></embed></object> <a href="{URL}">{URL}</a>
Help text :
Embed audio from SoundCloud into your post. Use the track URL, ex : [soundcloud]http://soundcloud.com/forss/speech-craft-no-sleep-til-dawn-remix-by-forss[/soundcloud]
edit :
Quite some time ago, I sent all the code necessary for some trivial BBCode, but I then got the reply that there was a general policy against inclusion of new codes. There wasn't much explanation from what I can remember.
And, ehr, now I noticed the link in the OP.