By default when services are up NO checks are done on the host check.
when a service is down nagios checks if the host is up by doing the check-host-alive check.
If a host is DOWN no notifications should be sent for the services on that host. If a host is down how could a service be running?
You want the notifications for the single services to be sent if the host is down? I think i just understood your request now...
Not sure it can be done... i think it could... BUT anyway you could use an eventhandler script that sends out "fake" emails for the services when the host goes down.