Think dirty: Conjure up a naughty scenario where the two of you are having sex. Keep it running through your heard, then glance at him while slowly stroking your bottom lip with your index finger. If you can pull it off, lower your head slightly as you're looking at him. Why? It lets him know that you're thinking something very naughty and makes him wonder what on Earth is going through your head. To really seal the deal, say something like, "Sorry, what were you saying? I got a bit lost there." It's particularly effective if he was saying something he thought you'd be mega-interested in (like the fact that he owns a private jet). NOTE: It's crucial with this one that you maintain eye contact, or it sends the opposite signal that you drifted off because you were bored.
Take it down a notch: Does this is all sound a bit contrived and girly for you? Then do any one of them in a more subtle way, working on his subconscious. The trick is to experiment with volume control and adapt them to suit you. (Practice in front of the mirror to get an idea of what the techniques look like.) Can't bring yourself to stroke your bottom lip? Look at his mouth while he's talking instead. Also watch his reaction: If he's clearly enjoying himself, feel free to up the ante and be more overt with the techniques. If he's shy or you're not sure, keep them simple and play them down a little.