To Whom It May Concern:
Thank you for your letter of [date of the rejection letter]. After careful consideration, I regret to inform you that I am unable to accept your refusal to offer me employment at this time.
This year I have been particularly fortunate in receiving an unusually large number of rejection letters. With such a varied and promising field of candidates, it is impossible for me to accept all refusals.
Despite [Name of the Company]'s outstanding qualifications and previous experience in rejecting applicants, I find that your rejection does not meet with my needs at this time.
Therefore, I will initiate employment with your firm immediately. I look forward to working with you.
Best of luck in rejecting future candidates.
Sincerely,
[Your Name]