gistfile1.cs

var basicTestTemplate = "{{mycustomhelper Person.Address.City}}";
var blockTestTemplate = "{{#mycustomblock Person.FirstName}} Hello world {{/mycustomblock}}";

Handlebars.Handlebars.RegisterHelper (
	"mycustomhelper", 
	(writer, context, arguments) => writer.Write (arguments [0]));

Handlebars.Handlebars.RegisterHelper (
	"mycustomblock", (writer, options, context, arguments) => {
		options.Template(writer, (object)context);
		writer.Write(arguments[0]);
	});

var data = new {
	Person = new {
		FirstName = "Bob",
		Address = new {
			City = "New York"
		}
	}
};

var basicTest = Handlebars.Handlebars.Compile (basicTestTemplate);
var blockTest = Handlebars.Handlebars.Compile (blockTestTemplate);

Console.WriteLine (basicTest (data));
Console.WriteLine (blockTest (data));
Console.Read ();