C# initialiser conditional assignment

In a c# initialiser, I want to not set a property if a condition is false.

Something like this:

ServerConnection serverConnection = new ServerConnection()  
{  
    ServerInstance = server,  
    LoginSecure = windowsAuthentication,  
    if (!windowsAuthentication)
    {
        Login = user,  
        Password = password  
    }
};

It can be done? How?