Take someone out in your Boxster who isn't too familiar with cars (mainly Porsches of course). Pull to the side of the road as if something feels wrong or you broke down. At this point pop the hood and act like you are looking for a problem. Then start bringing stuff out or tossing items and act like "What the hell is this doing in here?" Before hand you must stock the front trunk with many silly items such as old rags, balloons, pieces of metal, shoes, anything funny. The confused look on the passenger's face will be priceless. Nothing can beat the reaction from "Here is the problem!" and bringing your cat Whiskers from the trunk.
Note: If they think it is rear engine this could possibly work in the back too but may be a littler harder to pull off.