I don't think so. You have to be someones friend in order for them to be in your mafia (or "friends" in any facebook application).
When you add them, you should put them in a category so that later on down the road, you can delete them. and you can also ignore them so their crap doesn't show up on your wall. go to "Friends" (top left, blue bar) click on "all friends" in the drop down and you can put them into "Lists" (click on the "Create new list" button) for your existing mafia friends. and then go into your facebook "settings" up on the top right in the blue bar to figure all that out the 'privacy' stuff so their updates aren't bothering you.