http://www.gravityhelp.com/forums/topic/multisite-2#position-9 I didn't want to edit the plugin directly so tried to find an alternative way to display the main sites forms on sub sites. In the end I used the gravity forums shortcode filter. To pretty much output my own forms setting my own database prefix. I had trouble with the form submit so …

gistfile1.php

<?php
add_filter('gform_shortcode_form', 'gform_shortcode_form_mu_override',10,3);

function gform_shortcode_form_mu_override( $shortcode_string, $attributes, $content ){

    global $blog_id, $wpdb;

        $old_wp_prefix = $wpdb->prefix;
        $wpdb->prefix = 'wp_';

        require_once(GFCommon::get_base_path() . "/form_display.php");
        $new_form = GFFormDisplay::get_form($attributes['id'], $attributes['display_title'], $attributes['display_description'], $attributes['force_display'], $attributes['field_values'], $attributes['ajax'], $attributes['tabindex']);

        $wpdb->prefix = $old_wp_prefix;

        //replace the new forms action with one to the root site, rather than /sub-site/ which wouldn't process/submit
        $shortcode_string = preg_replace('/action=\'.*#/', 'action=\'/#', $new_form);

    return $shortcode_string;
}