SSL for custom domain WPMU subsite?

I see a number of threads but not clear which one would have the latest and most relevant information or a solution.

I have multiple subsites assigned to customers, each at their own custom domain name (using domain mapping plugin.) I am also using the Pro Sites plugin.

One customer wants SSL. Can it be done? Is it just a matter of getting a wildcard SSL or is there more to it? Please identify specific steps required…