Thanks guys,
I returned the guitar to my friend today. I came to work a bit earlier than him and placed the guitar case on his desk. A while later he came in and opened the case. First reaction: "OH!! What's that...?! ...*laughter*..."
He was really surprised and seemed to be very satisfied with the result. "Now it looks like a guitar again" he said and I think I ruined half of his work effort today, because he couldn't keep his hands off the guitar.
Job done, it is nice when you can make someone happy with these kind of small things in life.