I don’t think you can do this directly.
This is how I would go for it:
1. Create a TV (accessKey)
2. Create a chunk-template to format a row in WF, wich would look like this:
<li[+wf.id+][+wf.classes+]>
<a accesskey="[[getField? &docid=[+wf.id+] &field=`accessKey`]]" href="[+wf.link+]" title="[+wf.title+]" [+wf.attributes+]>[+wf.linktext+]</a>
[+wf.wrapper+]
</li>
And that’s it!
(I used getField snippet, which you can find here:
http://modxcms.com/getField-667.html)
I’m not sure about this solution. Any other suggestions?