How do I make Dapper Dommel insert an application generated primary key?

Suppose my entity is

public class AppUser
{
    string Id { get; set; }
    string Name { get; set; }
}

It looks like by default Dapper Dommel doesn't insert the Id field. It would generate SQL very close to this:

insert into AppUser (Name) values ("Dapper") select cast(scope_identity() as int)

This SQL is generated by using the Dapper Dommel Insert function like so:

using (var connection = new System.Data.SqlClient.SqlConnection(ConnectionString))
{
    connection.Open();
    connection.Insert<AppUser>(new User { Id = "someGuid", Name = "Dapper" });
}

I would like it to insert the Id column that I have provided a value for and also not perform the select cast(scope_identity() as int) query. That is, I would like something like this

insert into AppUser (Id, Name) values ("someGuid", "Dapper")

I can't seem to find this in the documentation. Does anyone know how to achieve this?