// Either from a config file or from a Config "Module" class:

ContainerBuilder builder = new ContainerBuilder();

builder.RegisterType<MyEmployerImpl>()
       .As<IEmployer>()
       .SingleInstance();

builder.RegisterType<MyContractorImpl>()
       .As<IContractor>()
       .InstancePerDependency();

SomeGloballyAccessiblePlace.Container = builder.Build();

// MyContractorImpl

class MyContractorImpl : IContractor
{
    private readonly IEmployer _employer;

    public MyContractorImpl(IEmplyoer employer)
    {
        if (employer == null) throw new ArgumentNullException("employer");
        _employer = employer;
    }
}

// Somewhere in your code:

var newContractor = SomeGloballyAccessiblePlace.Container.Resolve<IContractor>();