Unless you hold the stock yourself, it's in the "street name" and thus voting would be done with your stock broker as intermediary. So call your stock broker, at any time prior to the May 2 election. Obviously that means you want to call your broker this month. In a proxy battle, the same shares if held in "street name" can be voted many times, last vote counts.
For example, if Ribble owns shares currently and votes to keep Frank and his flunkies, then sells those shares to me this week, I can vote those shares for Clinton Group's nominees next week, and they will only count for Clinton Group, not Frank. But if I sell the shares back to Ribble after that, then he can vote the shares for Frank again. Last (before the election) vote counts.
I believe the only restriction is that you'd have to buy the shares at least 3 trading days prior to May 2. Just to be safe, I'd say April 26 is the last day one could buy SWC shares and still participate in the vote. I believe the above is correct, but again the best bet is to call your broker for details - it's part of their job to have someone at their firm that can tell you how the voting will work. I currently own 9,000 SWC shares long, and plan to vote them all for Clinton Group nominees (i.e. against Frank McAllister and his cronies on the board).
By the way, I believe you can also change your own vote, prior to the election. So if you vote your shares for Frank's bunch, then change your mind and want to go with Clinton Group, you still can.
I am basing this on the somewhat famous proxy fight at Hewlett-Packard, where dissident shareholders sought to block an acquisition of Compaq and presumably oust CEO/Chairwoman Carly Fiorina soon after. The vote was expected to be very close, and a large block of shares in a mutual fund owned by Deutsche Bank had been voted NO (against the merger, and by extension against Carly). Then H-P took out a $4 billion loan from Deutsche Bank (even though they had no imminent need for this money) at terms favorable to DB. And - to no one's surprise - DB then changed those NO votes to YES.
The H-P proxy vote for the Compaq acquisition narrowly passed, Carly kept her job for a few more years (until finally fired by the H-P directors, in a rare case of acting in shareholder interest, unlike the SWC directors). Unfortunately, that's how it works sometimes, which is why it's so hard to remove entrenched management - they can use the shareholder's own assets against them, to remain entrenched.