On the moment, when you want to add some external code to your project you need to use the integration studio. It creates some code with stubs for you, you can add your code in an external party code editor (like Eclipse or Visual Studio) and later on import that in Service Studio as just another action. It's great and it works. However, the downside of this is that you need to move from SS and deal with the Integrtation Studio and the code editor.
My idea enrolls around letting it happen in Service Studio itself; no need to switch away from your beloved visual programming environment.
With the help of a new widget, you drag/drop it to your canvas. You set the necessary properties in the property pane (or maybe on a central place) and then after a double click, just program your not-so-visual, plain text code in the code editor.
The code editor will contain the basic functionality you expect a code editor to have.
I have attached an image to further explain my idea.
P.S. This idea goes well with my other entry about making Service Studio a cross language IDE.