I don't think it is possible. The .php code behind the scenes looks like it automatically sets spoilers to a default:

[code]
function sp_filter_display_spoiler($atts, $content)
{
    global $spoilerID, $spVars;
    $original = $content;

    if (!isset($spoilerID))
    {
        $spoilerID = 1;
    }
    else
    {
        $spoilerID++;
    }

    $out = '';
    $out.= '<div class="spSpoiler">';
    $out.= '<div class="spReveal">';
    $reveal = sp_text('Reveal Spoiler');
    $hide = sp_text('Hide Spoiler');
    $out.= '<a id="spRevealLink'.$spoilerID.'" href="javascript:void(0);" onclick="spjSpoilerToggle(\''.$spoilerID.'\', \''.$reveal.'\', \''.$hide.'\');">'.$reveal.'</a>';
    $out.= '<input type="hidden" id="spSpoilerState'.$spoilerID.'" name="spSpoilerState'.$spoilerID.'" value="0" />';
    $out.= '</div>';
    $out.= '<div class="spSpoilerContent" id="spSpoilerContent'.$spoilerID.'">';
    $out.= '<p>'.$content.'</p>';
    $out.= '</div></div>';

    $out = apply_filters('sph_display_spoiler_filter', $out, $original);

    return $out;
}
[/code]