It sounds like you should split out your model into its own assembly and reference it from your MVC-application and WCF-application.
- YourApp.Data — Shared model and data access maybe
- YourApp.Web — If you want to share more across your web-apps
- YourApp.Web.Mvc
- YourApp.Web.WebService
If you want to do WebServices MVC-style maybe you should use MVC to build your own REST-application.