If there is a mixed skill level and you are looking to run a mini-tournament there are some fun things you can do that takes some of the skill out of it. A couple of ideas I've seen posted before...
Team Pinball - 2 people play at the same time, one for each flipper
"Blind" Pinball - Cover the lower 1/4 or so of the pinball machine with a piece of cardboard or something similar, like from the slings down
One Handed - You play with one hand behind your back