Caliburn.Micro EventAggregator Extension Methods

When working with the EventAggregator, I occasionally stumble upon situations in which I want to subscribe to multiple instances exposing the IHandle interface. It is not often, but happens enough that I got tired of the same code multiple times, and created a couple of extension methods to deal with this for me. I have posted the code up on GitHub as a Gist in case you find it useful as well.

Here is the code for your review:

As always, comments and suggestions welcome.