You will need to specify this in a style attribute on the <a> tag like this:
<li class="link">
<a style="width: 22px;" href="/menuwriter/index.php">Home Page</a>
</li>
If you are doing this on a dynamic menu like php, then you would need to go into your CSSMenuWriter > cssmw > menu.php and make the change like this:
<li><a href="<?php echo($assumedRoot); ?>index.php" style="width:22px;">Home Page</a></li>
Whatever you specify in the style attribute will overwrite any of the css that is applied to that element.