I usually use selfcert or the iis wizard to create ssl request or certificates. These are fine as long as you don’t have to install the certificates in multiple servers.
In that case you need to create a wildcard ssl certificate. I also wanted to avoid having to create certificates for each domain I was testing. It seems that the easiest way to be able to do this is to use certreq. This tool will create a request based on a configuration file that you can customize. Below is the sample I created for a certificate that can be installed on any machine of the domain and it also registers several domains.
This KBArticle is helpful but it doesn’t mention that if you are registering several domains the first one should be the wildcard FQDN.