Reply To: Custom field in search settings to appear dynamically

I’m sorry, I may have phrased incorrectly.

The code I gave does not resolve the issue – it is only a sample code to remove values from a frontend filter, based on the custom field name.
The $exclude variable needs to be filled with the values to exclude. That section needs to be custom coded. Perhaps to do a query on the meta table with a left join to get the union of meta fields that exist in both sets. Something like

add_filter('asp_pre_get_front_filters', 'asp_change_a_filter', 10, 2);
function asp_change_a_filter($filters, $type) {
    // Enter the custom field name
    $field = 'winery';
    // Get the custom field values to exclude from the filter
	global $wpdb;
    $exclude = $wpdb->get_results("
		SELECT DISTINCT(pm.meta_value) FROM $wpdb->postmeta pm
		LEFT JOIN  $wpdb->postmeta ppm ON (pm.post_id = ppm.post_id AND ppm.meta_key = '_stock_status' AND ppm.meta_value = 'instock')
		WHERE pm.meta_key = '$field' 
	", ARRAY_N);

    foreach ($filters as $k => $filter) {
        if ( $filter->type() == 'custom_field' && $filter->data['field'] == $field ) {
            $filter->remove($exclude);
        }
    }
    return $filters;
}

This should be really really close to an actual solution.