We mailed our DA letter to the KH. At the exact same time, we mailed one letter to one "sister" from the KH with whom we had a lot of contact with in the months prior to DA'ing. She had no clue what was coming, although she knew we were inactive. We sold/gave her a lot of stuff from our cleaning business, since we had just ended our business and she was just starting one. LDB also spent a lot of time with her giving her advice about the business.
(On a side note, she subsequently got counseled by the elders for coming over to our house to talk to LDB "alone" while I, the wife, wasn't home. Give me a break! LDB is in his mid-30's and this woman is in her late 60's! What did the elders think was going to go on in my absence? Talk about control freaks!)
Anyway, this lady was/is very nice and appreciative of our help and had talked about having us over for dinner (before she knew about our plans to DA). So we sent her a short letter explaining that we had sent our official DA letter and briefly explained why we DA'd. We also wanted her to know that we still really cared for her and our personalities and hearts had not changed because we DA'd. Also, since the elders were on her case already, we wanted her to know we would do anything we could if she needed some sort of defense against elder accusations. We've never heard from her or the elders since mailing the letters.
I think it's good to send at least one other person in the congregation (a 'common' person, non-elder) a letter briefly explaining why you DA'd and hopefully disarm any potential rumors.
Good luck with your DA'ing. For us, it's the best thing we could have done (besides never becoming assimilated to begin with!)