Empty Spaces Lyrics

[Backwards message:] "Congratulations, You have just discovered the secret message. Please send your answer to 'Old Pink,' Care of the funny farm, Chalfont..." - Roger Waters
"Roger, Caroline's on the phone..." - Unknown Voice
What shall we use
To fill the empty spacesPink - Empty Spaces - http://motolyrics.com/pink/empty-spaces-lyrics.html
Where we used to talk?
How should I fill
The final places?
How should I complete the wall?