Eliminating extra td elements in thead with 'left' or 'right' options

Suppose that I have a table with two rows in thead.  As far as I know, one suggested practice in this case is to use td elements in one row, like:

```
<thead>
    <tr class="col-nums">
        <td>1</td>
        <td>2</td>
        <td>3</td>
    </tr>
    <tr class="col-names">
        <th>Name1</th>
        <th>Name2</th>
        <th>Name3</th>
    </tr>
</thead>

Fixing the left or right two columns, for example, would be accomplished with:
new FixedHeader(table, {"left": 2});
new FixedHeader(table, {"right": 2});

Unfortunately, FixedHeader fails to remove the extra td elements in this case.  The fix seems to be straightforward.