WCF / ASMX :: Connect Client Certificate To An Account In A Membership Database

I have created a web service that authenticates with username and password, works fine.
Basically this one, http://msdn.microsoft.com/en-us/library/ff649647.aspx

Now I also want to connect to this web service using client certificates, works fine
http://msdn.microsoft.com/en-us/library/cc948997.aspx

But I would like to when authenticated via client certificates, connect that certificate to a user in the membership database. So that I can use Roles.IsUserInRole(...) and such.

I thought that, well if I implement a Custom certificate Validator http://msdn.microsoft.com/en-us/library/ms733806.aspx then I could check for example subject and map that against a created username in the membership database.

But in the class X509CertificateValidator public override void Validate(X509Certificate2 certificate) I don't have the same ability as when the user is authenticated
like

void OnAuthenticateRequest(object source, EventArgs eventArgs)
HttpApplication app = (HttpApplication)source;

Basically how can I do this

app.Context.User = new
GenericPrincipal(new
GenericIdentity(username,
"Membership Provider"),roles);
within
public override
void Validate(X509Certificate2 certificate)

and if that is not possible, can this be solved differently? Bottom line, how do I connect a client certificate to a user account in the membership database. Is there a MSDN article on how to do this?