this piece of music has been somewhat ellusice for me too.
I am a music producer and have been looking pretty damn hard for it myself - I came to the conclusion that it was a bespoke piece written specifically for Walls.
I was hoping to use it for a R&B Remix that I'm working on and have now played it myself using some wonderfully lush sounding neopolitan strings.
I should have the remix completed by the end of July and it will be avaiable to hear on my MySpace page
http://www.myspace.com/copasetickman
If you want to play it yourselves - it couldn't be easier:
G, A#, C, G, A#, C, D, C, A#, G,
Obviously this may not be the same key as the advert as I have transposed it to work in the song I'm working on - play around and you'll get it. Be sure to use nice rich sounds as it will sound doo doo otherwise.