[knot-resolver-users] How to use forwarding when recursion is failed?

Hi, Folks! I want to use GoogleDNS 8.8.x.x as fallback forwarder when domain's NS'es are down or inaccessible (for example, when network connectivity between me and NS is broken). Is it possible? policy.add(policy.all(policy.FORWARD({ '8.8.8.8', '8.8.4.4' }))) works well, but disables recursion at all. How to call it only after/when recursion is failed? WBR, Ilya