Using the Umbraco RegisterModel, how do I save custom properties from an input field?

Here's what I have done so far:

I created a Register Member macro using the relevant Umbraco snippet. I then added the macro to a page and saved. This registration macro works well right off the bat, even with custom properties. Here's the view logic that achieves this:

@if (registerModel.MemberProperties != null)
{
    foreach (UmbracoProperty t in registerModel.MemberProperties)
    {
        @Html.LabelFor(m => t.Value, t.Name)
        @Html.EditorFor(m => t.Value)
        @Html.HiddenFor(m => t.Alias)
        <br />
    }
}

I have two problems with this:

1. It spits out all properties, even ones I don't want
2. I have no way of re-ordering the fields

I figured it would be easy to solve this by simply removing the loop and adding the fields manually using the following code:

@{
    var firstNameMemberProperty = registerModel.MemberProperties.Find(x => x.Alias.Contains("firstName"));
}

//BeginUmbracoForm

@if (firstNameMemberProperty != null)
{
    @Html.LabelFor(m => firstNameMemberProperty.Value, firstNameMemberProperty.Name)
    @Html.EditorFor(m => firstNameMemberProperty.Value)
    @Html.HiddenFor(m => firstNameMemberProperty.Alias)
}

This code rendered the custom property field, firstName, just fine, but when I submit the form the property is never saved.

Can anyone tell me why? Is there a better method I should be using to have more control over my custom member properties when registering a member?