jQuery label 'for' attribute selector

I am using Remy Sharp's labelover plugin for jQuery and I would like to exclude a label with the attribute for and value nature.

Here's an example of the code working:

$(document).ready(function() {
    $('form.default label').labelOver('over');
});

and what I'm trying to do:

$(document).ready(function() {
    $('form.default label').not($('label').attr('for','nature')).labelOver('over');
});

Can anyone see where I'm going wrong? Feels like I'm pretty close to what I need to do.