Have you tried just creating a 25/75/240 grid and flattening it and then modifying the css for the 25% column to use the same classes as for the 240 column (probably some other small adjustments also needed)?
Hmmm, well, No but I'll give it a go. I really don't know how to do that but I need to learn I reckon. Is there anything in the how to section at vbulletin.com on doing that?
Is this the code that needs to be altered?
<grids>
<grid name="Two Columns + Sidebar (25%, 75%, 240px)" auxheader="0" auxfooter="1" addcolumn="1" addcolumnsnap="1" addcolumnsize="3" columns="8"><![CDATA[<div id="doc3" class="yui-tvb-r3">
<div id="bd">
<div id="yui-main">
<div class="yui-b">
<div class="yui-gf">
<div class="yui-u first yui-panel">
<ul class="list_no_decoration widget_list" id="widgetlist_column1">$column[1]</ul>
</div>
<div class="yui-u yui-panel">
<ul class="list_no_decoration widget_list" id="widgetlist_column2">$column[2]</ul>
</div>
</div>
</div>
</div>
<div class="yui-b yui-sidebar">
<ul class="list_no_decoration widget_list" id="widgetlist_column3">$column[3]</ul>
</div>
</div>
<div id="ft">
<div class="yui-u yui-footer">
<ul class="list_no_decoration widget_list" id="widgetlist_column4">$column[4]</ul>
</div>
</div>
</div>
]]></grid>
</grids>