Run time typed / Generic variable

I'm looking way to implement class similar to following, contain a constructor with two parameters, the second parameter is a Generic runtime typed.

I'm using.Net3.5 inside Unity 3D

public class Parameter
{
    private mParameterName;
    private T parameterValue; // runtime parameter

    public Parameter( string parameterName, string parameterValue ){}
    public Parameter( string parameterName, long parameterValue ){}
    public Parameter( string parameterName, double parameterValue ){}
}

any help in correct direction will be awesome. Thanks in advance.