WBR Alternative in XHTML

I've been using tags in the thead cells for my tables, so I can control where browsers break long words. This works great, but its not XHTML compliant. What is the best alternative to using the wbr tag, that is valid XHTML? Example:

<table>
  <thead>
    <tr><th>ThisIsAReally<wbr />LongWord<th></tr>
  </thead>
  <tbody>
    <tr><td>...</td></tr>
    <tr><td>...</td></tr>
    <tr><td>...</td></tr>
  </tbody>
</table>

quirksmode has the solution