Convert Expando Object based on runtime type?

I have something like

Car:Vehicle {}   
Truck:Vehicle {}

Database ORM return list that could contain either. Fetch < Vehicle > will lose sub class information. If I fetch object or dynamic, it will return list of ExpandoObject. Due the the underline framework restriction, I can't pass in generic T, only strings. So I have something like this:

Type type = Type.GetType("Car")

I can also create a typed List< Car > like so

var genericListType = typeof(List<>);
var specificListType = genericListType.MakeGenericType(type);
var list = Activator.CreateInstance(specificListType) as IList;

Not sure where to go from here. Reflection seems not very efficient, also can't add to IList. Any hint? Thanks.