Just sign the Form 2553 as the being the 100% shareholder. Technically, you are the shareholder of the corporation, and being the sole shareholder, you are the 100% shareholder.
The IRS wants to know basically that all the shareholders are giving consent to convert to a S corporation. Thus, if no shareholders have given consent by signing on Form 2553, they cannot approve the S corporation election.
Even if the 30 day period has gone, please sign the consent in the appropriate places and mail the IRS letter asap you might still be granted an S Corporation election.