WCF Custom Security Token - without certificate!

[Robertro]

Is it possible to enable message level security, create a custom Security
Token (with associated Serializer, ClientCredential, etc) but not require a
certificate?

I've taken the Custom Token example from the .Net 3.5 SP1 samples and I'd
like to remove the certificate code so I can see the trees for the forrest. I
want to start off with it working without any certificates.

Regards