Here's the simple solution.

Not everything has to be written with extension method in .NET code. One of the great things about MVC is it gives you easy access to construct your own HTML.  

With MVC4 you can get the id and name of the element on the expression tree with the helpers [`HTML.NameFor`][1] and [`HTML.IdFor`][2]



    <select name="@Html.NameFor(Function(model) model.CityId)"
            id="@Html.IdFor(Function(model) model.CityId)"
            class="location_city_input">
        @For Each city In Model.Cities
            @<option value="@city.Value"
                     @(If(city.Value = Model.CityId, "selected", ""))
                     data-geo-lat="@city.Lat"
                     data-geo-lng="@city.Lng"
                     data-geo-zoom="@city.Zoom">
                @city.Text
            </option>
        Next
    </select>

Assuming `Model.Cities` is a collection of items that expose each of those properties.  Then you should be all set.  

If you want reusability, consider making it an editor template for anything that is an Enumerable of Cities

[1]: http://msdn.microsoft.com/en-us/library/hh833703.aspx
[2]: http://msdn.microsoft.com/en-us/library/hh833709.aspx

Is there anyway to have a SelectList prepopulated on ViewModel with data-attributes ?

I want to do 

    @Html.DropdownListFor(m=> m.CityId, Model.Cities);

so it generates code like :

    <select id="City" class="location_city_input" name="City">
        <option data-geo-lat="-32.522779" data-geo-lng="-55.765835" data-geo-zoom="6" />
        <option data-geo-lat="-34.883611" data-geo-lng="-56.181944" data-geo-zoom="13" data-geo-name="Montevideo" data-child=".state1" value="1">Montevideo</option>               
        <option data-geo-lat="-34.816667" data-geo-lng="-55.95" data-geo-zoom="13" data-geo-name="Canelones, Ciudad de la Costa" data-child=".state41" value="41">Ciudad de la Costa</option>
    </select>

