For starters, you can advise him to seek access to the company's underlying records by exercising his investor inspection rights. If you've never heard of inspection rights, join the crowd. The Delaware Supreme Court recently marveled at how few investors know or use these important rights.
State laws guarantee investors the right to inspect and copy corporate records.
The statutes codify rights that date back to 16th century England. In cases where a fiduciary abuses its duties to the entity and then hides its misdeeds from the passive investor by imposing an information blackout, the right to seek court ordered access to the books and records maybe the passive investor's only recourse. The inspection statute in this particular company's state of incorporation governs. Because most publicly traded companies incorporate in Delaware, its statute gets the most use. Also, under the Delaware statute, if the corporation refuses or ignores the demand for inspection, the stockholder can petition the Chancery Court for a summary order requiring the company to comply.