Reference an internal class from a Windows Workflow Activity

Question

I'm creating a custom Workflow activity for use within TFS2010. In the same assembly I have a XAML activity and a C# code activity. The XAML activity references the code activity.

When the assembly is deployed to our clients, I only want them to be able to use the Workflow activity. The code activity is of little use by itself and would no doubt confuse them.

I thought the logical way to do this would be to set the code activity class to internal: the XAML is in the same assembly and should be able to access it. However, when I do that I get an error in the XAML saying that the type can't be found in the assembly.

Is there a way to make activities internal/hidden?