It's a good idea to try this out on the first level, but the ghosts DO take a while to emerge. If you've played into the mid teens (you can select any level you've played before), you can find some levels where the ghosts come out almost instantly, and stay blue for a while after eating a power pellet.
When you've found the level you want to try this on, wait until at least three ghosts are following you. I like to do a loop around the stage to sort of "clump" the ghosts up. When you have them sort of near each other, head for a corner where you'll see one of the larger power pellets. At this point, let Ms. Pac-Man move into a wall so that she's completely stopped (as close to the power pellet as possible). Wait until the ghosts are about to reach you (until you see the whites of their eyes, heh), and dive for the pellet.
If you've set things up like this, you should have no problem eating three, almost instantly. This strategy also works for four ghosts, of course.