I sent a GW letter to 3 different addresses for Macy's. I haven't gotten a reply yet, but when I do, if I get a denial I'll let it fuel the fire to write more letters and find out who is the next higher-up person to contact.
One thing I learned in general when trying to get info like that is to call and say "I wanted to write a letter explaining how much an employee helped me and I want to nice write a positive letter about it. What's your supervisors name, and the person above him/her too!" Ensure the person its a positive letter and not bad. Just make sure then when you write a GW letter, you do include something positive in it to honor what you said. If they're going to do GW for you, you might as well do GW for them too.