Proposed change to save logic: Add a filter to the handle_submission function.

I.e. to prevent GF from saving to it's own tables. In form_display.php modify the handle_submission function as follows to allow a developer to save the data in a custom data-store:

public static function handle_submission($form, &$lead, $ajax=false){

        //insert submissing in DB
        $disable_insert = apply_filters("gform_disable_field_insert_{$form["id"]}", apply_filters("gform_disable_field_insert", false, $form, $lead), $form, $lead);
        if ( !$disable_insert ) {
        	RGFormsModel::save_lead($form, $lead);

        	//reading lead that was just saved
        	$lead = RGFormsModel::get_lead($lead["id"]);
	}
	else {
		do_action( "gform_custom_field_insert", $form, $lead );
		do_action( "gform_custom_field_insert_{$form["id"]}", $form, $lead );
	}

        $disable_post = apply_filters("gform_disable_post_creation_{$form["id"]}", apply_filters("gform_disable_post_creation", false, $form, $lead), $form, $lead);
        if(!$disable_post){
            //creates post if the form has any post fields
            $post_id = RGFormsModel::create_post($form, $lead);
        }

        //send auto-responder and notification emails
        self::send_emails($form, $lead);

        //display confirmation message or redirect to confirmation page
        return self::handle_confirmation($form, $lead, $ajax);
    }