Is it possible to add a property to a type, via a DynamicProxy?

Question

I'm using Castle DynamicProxy to create a proxy of a given type at runtime - including a couple mixins.

I'm trying to figure out if it's possible to also add arbitrary properties to the proxy, e.g.:

class BaseType
{
  string Foo { get; set; }
}

and at runtime, I create a new type, that would look like this:

class BaseTypeProxy3848484etc
{
  string Foo { get; set; }
  OtherType Bar { get; set; }
}

In theory, it seems like this should be possible-- maybe I'm just not seeing how to do it with Castle... Any thoughts? Thanks!