When ever my brother gets one of these calls he goes to the kitchen, gets a lighter, a bottle or glass of water and a straw. While talking to the scammers he asks them to "just hold on a sec", flicks the lighter once or twice, puts the straw in the bottle/glass of water and blows for a few seconds. He then fake coughs, loudly and repeatedly. When he picks up the phone again he says,"Hello?Who's this again?".
He does this several times, probably every two minutes or so. Each time he answers in a more vague and forgetful fashion. Some of the scammers get quite upset: "What are you doing, sir? I am trying to help you with your faulty computer. I don't understand what is going on sir". He just answers with a very vague (and Chong-like), "Wha'?"
Eventually they get the ***** and hang up.