There are two possibilities:
<script type = "text/javascript">
window.onload = function() {
sbar_toggler.toggle();
};
</script>
<script type = "text/javascript">
jQuery(document).ready(function() {
sbar_toggler.toggle();
});
</script>
Put either one of these in the HEAD section of main.php
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Edit:
I should add that I prefer the second solution.