How to create an SSL certificate for more than one subdomain?
Yes, use *.myserver.net as common name.
This is called wildcard certs and there are large number of howtos finding with this keyword.
Here is one of them: https://web.archive.org/web/20140228063914/http://www.justinsamuel.com/2006/03/11/howto-create-a-self-signed-wildcard-ssl-certificate
Update: if you want cert to match root domain as well (myserver.net), then you should use Subject Alternative Name extension. When generating cert using openssh enter '*.myserver.net/CN=myserver.net' as Common Name.
Compatibly is good enough, unless you have an ancient browser.