I'm not sure if this works, but can you just add a class to the TD and then use the regular css 'max-width=xx' i.e.
td.classname{max-width:500px;}
If this wont work can you add a div inside the TD and give the div a max width? like this:
css:
table tr div.stylename{max-width:500px;}
html:
<table border="1">
<tr>
<div class="stylename">
<td>row 1, cell 1</td>
<td>row 1, cell 2</td>
</div>
</tr>
<tr>
<div class="stylename">
<td>row 2, cell 1</td>
<td>row 2, cell 2</td>
</div>
</tr>
</table>
Maybe another way could be to use php, as in set the width of the TD to a php variable which is connect to a max width setting ?
Goodluck