KeyRemap4MacBook config mapping capslock to escape (control when used as a modifier).

private.xml

<?xml version="1.0"?>
<root>
    <item>
        <name>F19 to Control_L</name>
        <appendix>(+ When you type F19 only, send Escape)</appendix>
        <!-- Note: identifier has "jis_" prefix for compatibility. -->
        <identifier>private.controlL2controlL_escape</identifier>
        <autogen>--KeyOverlaidModifier-- KeyCode::F19, KeyCode::CONTROL_L, KeyCode::ESCAPE</autogen>
    </item>
</root>