Can a company be an 'S' corp for tax purposes outside of being a corporation?

The company is already an LLC registered with the state as sole proprietor, pass through-disregarded entity. (This means that it is not considered a 'C' corp nor an 'S' corp).

A).I have been told by a CPA that it is possible to file 'S' corp status only for tax purposes outside of being deemed a corporation (Form 2553 without filing f8832).

B). I have been told by another CPA that the IRS will not acknowledge this status at tax time if the company is not a corporation.

So my question is whether I can be an 'S' corp for tax purposes outside of being a corporation?

Thanks in advance.