Is There a One-Time Special Dividend as a Means of Returning Capital to Shareholders?

Berkshire Hathaway's Warren Buffett says it is difficult to determine which companies are pure and which ones aren't. A one-time special dividend could be a useful option for returning a larger chunk of Berkshire's excess capital to shareholders without the implied promise to keep paying a regular dividend forever. The drawback with the special dividend though is that it would lead to an immediate decline in book value and book value for share whereas a larger Sherry purchase effort while depressing book value would reduce Berkshire's share count limiting the impact on book value forshare.