Just add code to your main class to select the appropriate startup object based on some set of options. Something like:
static void Main(string[] args)
{
string opt = args[0];
switch (opt)
{
case "foo":
Console.WriteLine("foo case");
FooClass foo = new FooClass();
foo.main();
break;
case "bar":
Console.WriteLine("bar case");
BarClass bar = new BarClass();
bar.main();
break;
default:
Console.WriteLine("No case");
break;
}
}