Webplayer project with hidden and exposed code?

Hi, I'm currently working on a project where there is base code and client-specific code. The project is a WebPlayer-based project. I'd like to provide my client with the client-specific code so they can maintain and update it per their needs, (and obviously do builds on their own) but I don't want to expose our base code. I know that If this were an .exe project I could wrap the base code in dlls, but WebPlayer applications cannot integrate with dlls outside of the security sandbox. Is there an analogous packaging framework for WebPlayer-based projects? Or any other solution I'm not considering? Thanks, Eric