Great idea! I've made an attempt in CSS, probably it would be easier with Javascript (but I don't know how to modify an extension). Add this to your Custom CSS section:
.z0 {
height: 15px !important;
padding-top: 0px !important;
padding-bottom: 6px !important;
}
.z0>.J-Zh-I {
background: transparent !important;
cursor: pointer !important;
border: 0px solid !important;
display: block !important;
width: 100% !important;
text-align: left !important;
color: #222 !important;
-webkit-border-radius: 0px !important;
float: left !important;
}
.z0:hover {
background: #E3E4E5 !important;
}
It works best with Minimalist Theme, if you use another skin you'll probably need to change the colors.