How can I invoke a method accepting Action

I am using Automapper where I am trying to invoke following method:

 **IMappingExpression ForMember(string name, 
    Action<IMemberConfigurationExpression> memberOptions)**

In second parameter Action contains an interface which has method

 **void MapFrom<TSourceMember>(Expression<Func<TSource, TSourceMember>> 
    mapExpression)**

For this method I have created local method which returns

expression<func<object,string>>

Now I am confused how can I dynamically invoke ForMember method by passing the required parameters I have.

Following is the expected result I want to achieve dynamically:

**map.ForMember(x.Key, opt => opt.MapFrom<string>(LocalMethod<object>(x.Value)));**

Where map is object of Automapper's configuration and LocalMethod returns an expression is as following:

**public static Expression<Func<T, string>> DefaultFilter1<T>(string fieldName)
{ 
}**