it would be completely okay for me to have the man guest i am bringing to my room leave his id when the lobby size is lets say that of suriwongse hotel. But if its gonna be sprawling like that of conrad's thats a different matter.
the only way to be discreet is what khun TP has mentioned. i.e. have the registered guest leave the unregistered guest's id at the reception. and hopefully everyone in of the hotel employee are discreet enough and not have that knowing smile in the morning when they greet you "good morning mr xxx".
