Try sending your letter/questions marked "Confidential" to the WTS with a stipulation in your inquiry saying that the local BOE are NOT to be contacted.
Simply note that you implicitly trust the letter desk/service department/writing department in this regard and to address your concerns directly without involving your local BOE. State clearly in your letter that if they were to copy a letter to your local BOE, then the WTS at its highest level cannot be trusted with confidential matters. State that all matters in your letter are addressed to the department only and it is confidential while quoting Proverbs 25:9,10.
Attach to that a copy of the Questions from Readers W71 4/1 "Christians keeping certain matters confidential ~ Proverbs 20:19"
You will then truly find out if the WTS is truly trustworthy and respectful for your request. If they are reluctant to do as you suggested, then they should reply back to you directly stating such without copying in the BOE.
However, if they do send a copy of the letter to your local BOE and these elders approach you with it, then you can gasp for air, perhaps cry out in anquish while in distraught terror that your trust was betrayed by Jehovah's annointed one while pointing out your copy of the letter in their hands with your instructions and with the big "Confidential" lettering on the top. Let them know that you now feel depressed and need time to pray to Jehovah for strength to recover from the betrayal.
After that......presume your fade.
Alligator Wisdom (aka Brother NOT Exerting Vigorously)