That's not supported per se, but I just made a quick test and it seems it's pretty easy to emulate with standard HTML.  Example:

<a class="hotspot" accesskey="b"
   onfocus="this.blur(); this.onclick();"> <!-- this line is for IE -->
  <u>B</u>ring it on
</a>
...
<ul id="menu">
  <li class="context-class-a-hotspot context-align-bottom">
    ... context menu content ...
  </li>
</ul>

Look, we just made a menu that triggers upon ALT-B. :-)

Hope this helps.