How to display constant values using custom-columns format of kubectl?

I have multiple clusters and I want to check which ingresses do not specify explicit certificate. Right now I use the following command:

~$ k config get-contexts -o name | grep -E 'app(5|3)41.+-admin' | xargs -n1 -I {} kubectl --context {} get ingress -A -o 'custom-columns=NS:{.metadata.namespace},NAME:{.metadata.name},CERT:{.spec.tls.*.secretName}' | grep '<none>'
argocd               argo-cd-argocd-server    <none>
argocd                argo-cd-argocd-server                                <none>
reference-app         reference-app-netcore-ingress                        <none>
argocd                  argo-cd-argocd-server                 <none>
argocd         argo-cd-argocd-server   <none>
test-ingress   my-nginx                <none>

~$

I want to improve the output by including the context name, but I can’t figure out how to modify the custom-columns format to do that.