Easiest way to keep podcasts and music on separate drives?

I just got a new MacBook Air and I'm struggling with iTunes library management on a small hard drive. I picked up a USB drive to store my large iTunes library (around 250gb). For music and movies, this is fine. However, I update podcasts far more often... at least twice a day. Hooking up the USB drive is a cumbersome process, so I'd like to avoid the need for this.

Here's what I'd like to accomplish: I'd like my podcast and audiobook library to live on my MacBook Air internal hard drive so that I can sync my iPhone up multiple times per day with updated material. And I'd like to keep my music and movies on the external drive because I only need to sync up my iPod classic once every week or two.

Right now everything is on the external drive. I want to come up with a system that eliminates the chance of me messing up my very large iTunes library. So far I've come across solutions like manually managing the library (which I'd like to avoid) and using software called TuneSpan which fools iTunes into thinking that everything is on a single drive. I'm not sure which is the best path to take. Anyone have any thoughts on this? What is the easiest, lowest maintenance way to get the job done?

Thanks in advance.