Formbuilder and foreign keys HELP

here goes..a parent DO wants to create a child DO, the new_child page has the parent FK in the URL which i can GET. I want to insert using the parents FK but i do not want the FK to be edited in the new_child form, i have tried a few diffrent options from hidden elements to non editable elements but it wont insert, how do u guys get around this?.. i also tried to force the insert..no good. If i allow the FK to be edited it inserts correctly

i fixed this..finally with this work around. In my child DataObject i added this :-

function preGenerateForm(&$fb) {
$el = HTML_QuickForm::createElement('hidden',
'parent_id');
$el->setValue($_GET['parent']);
$this->fb_preDefElements['parent_id'] = $el;
}

now where cooking...