SSL and Domain Mapping

I have SSL on the main domain but if the site (maindomain.com/usersite/) has added a mapped domain and needs to send encrypted forms, we get an SSL error because the mapped domain itself doesn't have an SSL certificate.

I'm happy to offer SSL certificate installation for the mapped domains but would the certificate need installing on the host where the domain is mapped from or on my server where the domain is mapped to?

I want to make it as simple for the user as possible to add SSL to their site.

Thanks.

Martin