Dynamic LINQ: GroupBy for MongoDB queryable collection

Question

I am trying to do a MongoDB aggregate using LINQ, with the MongoDB .NET Driver version 2.1 and .NET 4.5, using ScottGu's Dynamic LINQ library.

This is a simplified schema for the data stored in MongoDB:

{
     "_id" : "151207.01.02", 
     "project" : "SomeRandomProject", 
     "material" : "Azbantium", 
     "process" : "Paintball",
}

I have successfully used this to build a sort query with the following code (Where MyType is a POCO class used for MongoDB):

public static List<string> DynamicOrderAggregate(string parameter)
{
    var client = new MongoClient(connectionString); // a static value not shown
    var db = client.GetDatabase(database); // also a static value not shown
    var col = db.GetCollection<MyType>(collection);

    List<string> orderListString = new List<string>();

    IQueryable<MyType> colQueryable = col.AsQueryable();

    var orderedList = colQueryable
            .OrderBy(parameter)
            .Select(parameter);

    foreach(var item in orderedList)
        orderListString.Add(item)

    return orderListString
}

This yields an aggregate equivalent of this when I look at the orderedList variable when debugging when inputting "material" as the parameter:

{aggregate([{ "$sort" : { "material" : 1 } }, { "$project" : { "material" : "$material", "_id" : 0 } }])}

And I am able to get a list of "materials" for each run.

However, when I try a group query using the following code (using the suggestion from this post: How to use GroupBy using Dynamic LINQ):

public static List<string> DynamicOrderAggregate(string parameter)
{
    var client = new MongoClient(connectionString);
    var db = client.GetDatabase(database);
    var col = db.GetCollection<MyType>(collection);

    List<string> groupListString = new List<string>();

    IQueryable<MyType> colQueryable = col.AsQueryable();

    var groupedList = colQueryable
        .GroupBy(parameter, "it")
        .Select(String.Format("new (it.Key as {0})", parameter));

    foreach(var item in orderedList) // exception occurs here
        groupListString.Add(item)

    return groupListString
}

I'm seeing in the groupedList variable with an empty bracket and the query in some generic form:

{aggregate([]).GroupBy(Param_0 => Param_0.material, Param_1 => Param_1).Select(Param_2 => new DynamicClass1() {material = Param_2.Key})}

And I'm getting the following exception:

An unhandled exception of type 'System.NotSupportedException' occurred in MongoDB.Driver.dll

Additional information: The method GroupBy is not supported in the expression tree: aggregate([]).GroupBy(Param_0 => Param_0.material, Param_1 => Param_1).

I know that the .NET driver is relatively new. I really do need to be able to do dynamic queries that include grouping operations. Can anyone please advise?

Thanks kindly!

-- Ari