Dynamically add properties and its value to existing class comparing list of string

I came across a situation where I have a property class which has list of mandatory properties declared already(say class name may be Employee). Now I read list of other required properties from CONFIG file and add property and its value to the existing class, say Employee(another service will provide me a bunch of records, among them I need to retrieve value only which is configured in CONFIG file).

Can anyone suggest me the approach to implement this?