Passing Around Endpoints

Can I construct a proxy object on one machine and pass it to another?

No, there's no concept in WCF of sending a fully constructed proxy object from one place to another. Consider that there are two different things that "passing" a proxy object could mean: passing a reference to the object or passing a value by constructing an equivalent object in another location.
If you passed a proxy by reference, then what you really would be doing is sending messages from your local machine to the remote machine on each invocation, to be sent by the real proxy. However, that's just a service that forwards messages between the two proxies, and that's something that you can build yourself.

If you passed a proxy by value, then what you really would be doing is sending some description of the proxy to be created locally. Again though, that is something that you can build yourself by passing the endpoint description for the proxy you want to recreate and constructing a local proxy factory.

Next time: One Shot Serialization