You want to use SVG Filter effects to bevel arbitrary SVG Content.
Here's an example with two versions of a bevel:
http://jsfiddle.net/rcd5L/
<svg xmlns="http://www.w3.org/2000/svg" viewBox="-10 -10 120 100">
<filter id="Bevel" filterUnits="objectBoundingBox" x="-10%" y="-10%" width="150%" height="150%">
<feGaussianBlur in="SourceAlpha" stdDeviation="3" result="blur"/>
<feSpecularLighting in="blur" surfaceScale="5" specularConstant="0.5" specularExponent="10" result="specOut" lighting-color="white">
<fePointLight x="-5000" y="-10000" z="20000"/>
</feSpecularLighting>
<feComposite in="specOut" in2="SourceAlpha" operator="in" result="specOut2"/>
<feComposite in="SourceGraphic" in2="specOut2" operator="arithmetic" k1="0" k2="1" k3="1" k4="0" result="litPaint" />
</filter>
<filter id="Bevel2" filterUnits="objectBoundingBox" x="-10%" y="-10%" width="150%" height="150%">
<feGaussianBlur in="SourceAlpha" stdDeviation="0.5" result="blur"/>
<feSpecularLighting in="blur" surfaceScale="5" specularConstant="0.5" specularExponent="10" result="specOut" lighting-color="white">
<fePointLight x="-5000" y="-10000" z="0000"/>
</feSpecularLighting>
<feComposite in="specOut" in2="SourceAlpha" operator="in" result="specOut2"/>
<feComposite in="SourceGraphic" in2="specOut2" operator="arithmetic" k1="0" k2="1" k3="1" k4="0" result="litPaint" />
</filter>
<rect width="100" height="40" filter="url(#Bevel)" />
<rect y="50" width="100" height="40" filter="url(#Bevel2)" />
</svg>