in the webassist/plugins/admin_menu/menu.php file, change:
<?php if(WA_Auth_RulePasses("Super Administrator")) { ?>
<li><span><a href="../../../admin/admin_settings.php">Settings</a></span></li>
<li><span><a href="../../../admin/design.php">Design</a></span></li>
<?php } ?>
to:
<?php if(WA_Auth_RulePasses("Super Administrator")) { ?>
<li><span><a href="../../../admin/admin_settings.php">Settings</a></span></li>
<?php } ?>
<li><span><a href="../../../admin/design.php">Design</a></span></li>
how you display the coupon is up to you. you could use the content management system to show the coupon as a news article or add it to the Home Page -> Site Message section.