Form Helper default values from URL

Question

I have a form with method=GET.

echo $this->Form->create(NULL, array('type' => 'get'));
echo $this->Form->input('a');
echo $this->Form->input('b');
echo $this->Form->end();

But when calling formpage/?a=1&b=2 the input fields are not set with those values. Is there a way to pass $this->request->query into the form helper to set those defaults at once?