Setting parenthesis as a negative value

Hi, I have a number of tables that use parenthesis to represent a negative value and have been trying to get this to work within the 'Ignore text plugin' (link below).

http://www.datatables.net/forums/discussion/22343/new-sorting-plugin-sort-by-any-number-ignore-text.

I have tried replacing opening parenthesis with a minus symbol so that it reads the character as a negative value but this doesn't seem to have worked.

I've put a fiddle together as an example...

http://jsfiddle.net/Adam84/ot9doh27/1/

Any help is much appreciated!