Code Contracts: How to deal with inherited interfaces?

Question

I'm using MS Code Contracts and have run into a snag with using interface inheritance and ContractClassFor attributes.

Given these interfaces and contract classes:

[ContractClass(typeof(IOneContract))]
interface IOne { }
[ContractClass(typeof(ITwoContract))]
interface ITwo : IOne { }

[ContractClassFor(typeof(IOne))]
abstract class IOneContract : IOne { }
[ContractClassFor(typeof(ITwo))]
abstract class ITwoContract : IOneContract, ITwo { }

Let's say that IOne and ITwo are substantial interfaces. So IOneContract would have a significant amount of code in it for the necessary checks.

I don't want to duplicate all of that in ITwoContract for the IOne interfaces. I only want to add new contracts for the ITwo interfaces. Inheriting one contract class from another seems the likely way to reuse that code. Yet I get the following error:

EXEC : warning CC1066: Class 'ITwoContract' is annotated as being the contract for the interface 'ITwo' and cannot have an explicit base class other than System.Object.

Is this a limitation in Code Contracts or am I doing it wrong? We have a lot of interface inheritance in our project and this feels like a deal breaker for Code Contracts if I can't figure out how to work around this issue.