Function set_value() not working as expected

[eluser]w1n78[/eluser]
i'm trying to use jbreitweiser's fix (http://ellislab.com/forums/viewthread/96617/P15/#689642)

but rather than edit the functions in /system/libraries/Form_validation.php file i created a /application/helpers/MY_form_helper.php file and pasted the script.

i am getting a "Fatal error: Using $this when not in object context..." error. the line where the error is occurring has the following...

Code:

if ( ! isset($this->_field_data[$field]))

any ideas?