Far, far better is to attack your local CBS affiliate who carried the Rather filth. Threaten to oppose the extension of their license the next time it is up for renewal by the FCC. Threaten to write to the FEC asking for civil penalties against the local station for running political messages pretending to be news (Rather's nightly "defense" is clearly that).
The affiliates can bring far more pressure on CBS and Viacom that a flood of letters. The affiliates can apply pressure; your letters just prove folks are watching/talking about CBS.
Woaaahhh there horsey, contacting the local affiliates is a VERY effective means to change CBS, but under Sarbanes-Oxley do NOT discount the effectiveness of director contact.
Unlike Union Contract negotiations, these guys have PERSONAL LIABILITY for shareholder equity. LEGAL liability as of Sarbanes. So simply let them know that while a "coming clean" might diminish some shareholder equity in the short term, that the longer this controversy continues, in the face of all of the damning evidence, the worse for shareholder equity.
Acting now, while possibly negatively impacting shareholder equity in the very near term, also removed the liability because while shareholders may not be happy, the Board has moved quickly to restore the reputation and integrity of CBS which is ALWAYS in shareholders, AND THE PUBLIC'S interests.
And if they do not act to correct the malaise at CBS, they can be personally liable for any loss in shareholder equity so long as the controversy is not resolved.
They have a DUTY to act.