Hi,
Well. not exactly but you can ignore products that are not in stock, please check this tutorial
Removing filter values is a bit more difficult, but doable programmatically via the frontend filters API.
This could be a good code skeleton to start with. All you need to implement is to get the custom field values as an array into the $exclude variable, which you want to remove from the filter, the rest should do the code itself.
add_filter('asp_pre_get_front_filters', 'asp_change_a_filter', 10, 2);
function asp_change_a_filter($filters, $type) {
// Enter the custom field name
$field = 'custom_field_name';
// Get the custom field values to exclude from the filter
$exclude = array('value1', 'value2');
foreach ($filters as $k => $filter) {
if ( $filter->type() == 'custom_field' && $filter->data['field'] == $field ) {
$filter->remove($exclude);
}
}
return $filters;
}