[Subject: Normally bold, summarizes the intention of the letter] -Optional-
It is indeed a great pleasure and opportunity for me to have been appointed as honorary chairperson to your respected firm. However, I regret to inform that my participation in this regard will be limited to your utilizing my name only for promotional activities as my full fledged participation is not possible owing to other obligations. However, I shall stay in constant touch and try to keep myself updated regarding your achievements in your endeavor.
I wish you to be all the more successful and propose to extend as much of my services as is possible.