You can fake gradient transitions using drop shadows!
For instance, from one of my pages:
c { 
color: #FFF;
background: #000;
border-style:solid;
border-color:#CCC;
border-width: 0 0 0 1px;
box-shadow: 2px 2px 2px #555, inset 0 25px 20px -10px rgba(255, 255, 255, 0.3),
    inset 0 -15px 20px -10px rgba(0, 0, 0, 0.15);
-moz-box-shadow: 2px 2px 2px #555, inset 0 25px 20px -10px rgba(255, 255, 255, 0.3),
    inset 0 -15px 20px -10px rgba(0, 0, 0, 0.15);
-o-box-shadow: 2px 2px 2px #555, inset 0 25px 20px -10px rgba(255, 255, 255, 0.3),
    inset 0 -15px 20px -10px rgba(0, 0, 0, 0.15);
-webkit-box-shadow: 2px 2px 2px #555,
    inset 0 25px 20px -10px rgba(255, 255, 255, 0.3),
    inset 0 -15px 20px -10px rgba(0, 0, 0, 0.15);
-moz-transition: background-color .5s ease; 
-o-transition: background-color .5s ease; 
-webkit-transition: background-color .5s ease-in-out; 
transition: background-color .5s ease;
}
Followed by:
c:hover {
color:#FFF;
background: #505;
position:relative;
top:1px;
box-shadow: -1px -1px -1px #555,inset 0 20px 20px -10px rgba(0, 0, 0, 0.15), 
        inset 0 -15px 20px -10px rgba(255, 255, 255, 0.3);
-moz-box-shadow: -1px -1px -1px #555,inset 0 20px 20px -10px rgba(0, 0, 0, 0.15),
    inset 0 -15px 20px -10px rgba(255, 255, 255, 0.3);
-o-box-shadow: -1px -1px -1px #555, inset 0 20px 20px -10px rgba(0, 0, 0, 0.15), 
        inset 0 -15px 20px -10px rgba(255, 255, 255, 0.3);
-webkit-box-shadow: 1px -1px -1px #555, inset 0 20px 20px -10px rgba(0, 0, 0, 0.15), 
    inset 0 -15px 20px -10px rgba(255, 255, 255, 0.3);
}
Here, you are essentially using an inset shadow as a Photoshop-like mask, causing a gradient effect on the underlying element. On hover, you invert the effect.