You could do this by hiding the other toolbar icons like in the example below.
.tundra .mendixToolbar_button {
width: 24x;
height: 20px;
margin: 0 7px 0 0;
padding: 0;
background: none;
}
.tundra .mendixToolbar_desktop,
.tundra .mendixToolbar_refresh,
.tundra .mendixToolbar_back,
.tundra .mendixToolbar_forward {
display: none;
}
.tundra .mendixToolbar_logout {
background: url(images/layout/icons/toolbar.png) no-repeat;
}
You probably have to play around with the toolbar image, or make seperate icons.