iPod Using Multiple Libraries At once

So I've searched high and low with no avail! I apologize for the repost if this is already solved amongst the threads but;

So simplified my setup is, MacBook and an external 250 GB USB HDD.

Problem: I want to put a majority (mostly the stuff I dont listen to, but cant get rid of) of my itunes library onto my external. I'm aware of the option(alt) key to create a new library and also to alternate between multiple libraries. So I was wondering if it were at all possible to have multiple libraries (one located on my MacBook and the other on my external) without having to alternate them. So I want them simultaneously displayed in the same window basically.

I hope thats coherent

let me know your thoughts!!

I can't believe I didn't think about that, thank you!
The only problem then is that while my external drive is disconnected the songs will still be listed in the library and when I have it on shuffle it will show the song doesn't exist and slow down the process of shuffling. Do you think there is a way to hide those songs while the external is disconnected?