Turn off the phone functions on your cell (often called 'airplane mode') but set the alarm clock function to ring in 15 minutes with a phone-style ring. If people are around but not coming over to your tale, answer the alarm clock ring and say "Yes, this is John Smith. Yes, the signing is on now at [give address]. Well, it is quiet right now, but I'm told to expect a crowd at [insert time about 45 minutes from now] once church gets out [or "school gets out", or "the cinema gets out",or insert other credible explanation]. Well, that's nice of you to say. Yes, I can put a copy aside for you, but I have already reserved quite a few copies (place hand on largest stack of books) so I could only hold it until, say [insert time 2 hrs from now]. Life changing? Why thank you! That's quite a compliment! I actually like this book even better than that one, but it is always nice to hear from people who enjoyed my previous work. Thank you! I look forward to seeing you. Be sure to introduce yourself. Goodbye.
Evil shilling idea #2.
Find a couple of friends with an impressively bulky video camera and tripod (or rent one), and have them show up about an hour into the signing. Have them 'introduce themselves' to you, then start 'setting up the camera'. This should take a while as the camera guy looks for the best angle and so on -- but every time a customer comes within range, the camera guy or the interviewer should wave them towards the author saying loudly, "It's okay, we'll be a while yet setting up, you go right ahead sir/madam!" As first couple of people are helplessly herded towards author, others will see a line up and a camera crew, and Bob's your uncle! If no one is coming in range at some point, camera crew 'rolls tape' and 'interviewer' interviews author about why he is coming to these small locations when obviously he is a much bigger draw, and author answers that he likes to mingle with his readers, etc. Interview refers vaguely to "given all the rave reviews you've received, how do you keep it all from going to your head" and similar traditional shilling. Once a crowd gathers to view interview, go into signing mode. Once that starts to dissipate, camera crew goes around to other customers asking if they can just get a shot or two of them with the author, thus funneling more people towards your table. Camera crew and interviewer eventually exit with much loud "it's been a total honour to meet you, I can't tell you how much I enjoyed your last book" etc. etc.