well you COULD do this. There is a javascript show/hide method generated for each spoiler. If you knew the name of the method (which is generated to be unique) you could invoke it.
You could then hide the show/hide button using the admin settings.
The actual call you would make is:
wpSpoilerToggle("id", true, "", "", "fast", false);
where id is the number you have to figure out. Look at the page HTML and search for "wpSpoilerToggle" to locate the first argument:
<a href="" onclick="wpSpoilerToggle("[b]spoilerDiv3a408001[/b]",true,"Show","Hide","fast",false); return false;" id="spoilerDiv3a408001_action" class="easySpoilerButton" value="Show" align="right" style="font-size:100%;color:#000000;background-color:#fcfcfc;background-image:none;border: 1px inset;border-style:solid;border-color:#cccccc; margin: 3px 0px 3px 5px; padding: 4px;">Show</a>