Jose,

I notice you keep coming up empty on this request.

Try
http://forums.microsoft.com/msdn/showforum.aspx?forumid=118&siteid=1

or
microsoft.public.windows.developer.winfx.indigo

I think the forum is your best bet.

That's such a specific wcf question...that the forums is probably your best
shot.

Then let me know me what you find! (by posting back here I guess).
I'm curious as well, just not as  curious as you are. (Well, not enough time
to check it).

Good luck.

Jose,

   This is the third time you have posted this.  Reposting in this manner
isn't going to make the answer come any faster.  On top of that, people are
going to see it, and probably start to intentionally ignore it.

   As for your particular issue, it's just not supported.  Brian McNamara
[MSFT] says:
We struggled with the tension of finding a programming model that was easy
to understand, and one that 'worked' without unexpected consequences. There
are lots of unusual edge cases that come about about as a result of multiple
inheritance which cause problems with many of the 'simple' approaches.
Here's one example. Suppose you have

[ServiceContract(Namespace="foo", CallbackContract=typeof(IBaseCB))]
interface IBaseC { ... }

interface IBaseCB : IBaseBaseCB { ... }

interface IBaseBaseCB { [OperationContract] void F(); }

Now if I create an endpoint of type IBaseC and allow reflection to walk up
both hierarchies, I'll end up with a callback operation F() in the contract
whose namespace is "foo".

Now suppose I write

[ServiceContract(Namespace="bar", CallbackContract=typeof(IBaseBaseCB))]
interface IOther { ... }

An endpoint of IOther has callback operation F() in namespace "bar". Now
suppose I do

interface IDerivedCB : IBaseCB { ...}

[ServiceContract(CallbackContract=typeof(IDerivedCB))]
interface IDerivedC : IBaseC, IOther { ... }

What is the namespace of operation F() of an endpoint of type IDerivedC?
There's no good solution; with IBaseC and IOther one has created contracts
which cannot reasonably be composed together.

In order to try to avoid most of these weird edge cases, we tried to keep
the model very constrained and simple. In general, when working with duplex
contracts, it is good to always define and refine the ServiceContract and
CallbackContract interfaces together; think of them as a single entity that
happens to be spread across two CLR interfaces. The [SC] is the
"authoritative" interface when it comes to getting info from attributes and
walking the inheritance hierarchy, while the CC is just an auxiliary
interface attached to a particular SC.