WF4 how to enable or disable dropdown(enum) argument based on previous/other dropdown(enum) value

Question

I have two drop down in my codeactivity property, I want to allow the user to select second drop down based on the first drop down selection. Please see my sample code :

public enum Services
{
    Human,
    Web
}
public enum ServiceType
{
    Soap,
    Rest
}


[Category("Input")]
    public Services ServicesFrom { get; set; }

    [Category("Input")]
    public ServiceType WebServices { get; set; }

From the above code when user choose HumanValue from ServicesFrom dropdown in property grid then I am not allow him to choose value from WebServicesDropDown. I want to disable the WebServices dropdown from property grid.

Any help appreciated!!
Thanks in Advance