I think that rather than expanding the layout to accommodate the wider navigation you can just decrease the size of the links in the top nav so that you can fit more of them in place.
The default value is 120px, so the number of entries you have in this menu will be multiplied by 120 for a total width of the menu. If you adjust this size to be smaller you can fit in a larger number of links without increasing the width of the page. You would make this adjustment in the following style:
CSSMenuWriter/cssmw_home/menu.css line 52
ul#cssmw_home > li > span > a {
background-image:none;
color:#FFFFFF;
display:block;
font-family:Arial,Helvetica,sans-serif;
font-size:14px;
font-style:normal;
font-weight:normal;
height:24px;
margin:5px 0 0;
padding-top:12px;
text-align:center;
text-decoration:none;
width:120px; /*this is the value to adjust*/
}
Just adjust the width to fit your needs. Also if the text is too large for a particular width you can adjust that with the font-size:14px; setting.