C# code : how to pass an instance of a value type to a method that takes an object as a parameter?

Yes. For example:
class CApplication
{
public static void Main()
{
int x = 25;
string s = "fred";

DisplayMe( x );
DisplayMe( s );
}

static void DisplayMe( object o )
{
System.Console.WriteLine( "You are {0}", o );
}
}
This would display:
You are 25
You are fred