<p>I have Visual Studio setup with a VSTO word project, and when I hit run it runs fine.</p>

<p>But, how do I setup a word document to use my code without having Visual Studio running?</p>

RubyCocoa is not supported at all on the iPhone. There is no bridge support library, and I do not believe there is any ruby interpreter on the phone.
You might be able to get it working in the simulator, it will not stop you from using OS X only libraries if you really try, but that still will not make it work on the iPhone.
If you really want to use RubyCocoa on the iPhone you will need to build ruby as a static library and port the bridge to the phone, which is doable, but would probably be very difficult.