tabelsorter with two header rows

tabelsorter with two header rows

Hi, i have two table header rows, one with Captions and one with controls, dropdown, checkbox etc like this:
thead
tr | Caption1 |  Caption2  |  Caption3  |
tr | [x] y/n  | [Opt. 1[v] | [Opt. 2[v] |
tbody
tr | Values1  | Values2    | Values3    |

How can i get tablesort to work only when clicking on the captions in row 1 and do nothing clicking on the controls in row 2?
Thanks in advance