How to pass WCF credentials in single request?

Question

I have this binding:

<customBinding>
    <binding name="b1">
        <security authenticationMode="UserNameForSslNegotiated">
            <secureConversationBootstrap />
        </security>
        <binaryMessageEncoding/>
        <httpTransport/>
    </binding>
</customBinding>

When I use a sniffer to see the calls, I see that this does 3 round-trips per call.

By looking at the requests I see that

• Message 1 is of type <t:RequestSecurityToken …>
• Message 2 is of type <t:RequestSecurityTokenResponse…>
• Message 3 is the real request

Is there a way pass credentials with the real message?

UPDATE Aug 23rd 2010: I still haven't found a solution to this problem.