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When choosing a shorter version of the URL, you cannot choose one that looks like another website that consumer's will recognize (which is up to interpretation).
The best thing to do is either call Google or contact them within your account and explain the situation and state the URL you would like to use.
I thought there was a help file on Google's site about this but can't find it at the moment.
Hence, I had to do away with the www and the .com extension. That way the url come to exact 35 characters. I have also filed an exception request for this.
Let me know your views.