In a custom module, have some code similar to this:
function MODULENAME_form_alter(&$form, $form_state, $form_id) {
if ($form_id == 'profile_node_form') { //change profile to be your content type
$form['body'][LANGUAGE_NONE][0]['#wysiwyg'] = FALSE;
}
}
body is the field name, you might need to change it if you're using a different / more fields.
It is probably best to name your module with something in the alphabet later than 'ckeditor' or use the moduleweights module to ensure your hook runs after ckeditor... I say probably because I haven't tested to see if this is an issue or not.