I agree with Brooke that the option of going suicide should be availiable, unless it can be shown that it's being used to get around the system. A lot of my chapter sisters did go suicide - they would have never taken a bid from another chapter. For myself, even though I was 75% sure I wanted ASA, I still wanted to explore my options and see if one of the other groups was a better fit. Then again, I had seen some friends go through rush hell, so I knew there was no such thing as a sure thing.
I think one of the things we could do to prevent it is use cold statistics. For example, if 70 girls suicided and only 10% of them got a bid, then say that, or better yet say "90% of women who 'suicide' do not receive a bid from the sorority of their choice.". If only 10% of those unbidded girls go on to participate in Greek life at all, say that too. I think rushees are so caught up in the excitement and even though they hear about other people not getting bids, think "that won't happen to me." Like JAM pointed out they're still thinking on high school level. Using statistics like that might sound negative, but it's no different than reading the college guides and seeing that Harvard, for example, only accepts 50% of applicants. With those odds, if you place all your bets on Harvard, you're either very optimistic or very stupid. Rushees need to understand that going suicide is a serious matter and it could have very bad consequences. Duh, that's why we call it that!
I don't think just saying "keep an open mind" will make anyone do it, but maybe if they realize that close-mindedness can keep them out of Greek life altogether, they'll give some of the sororities that they dismissed a second look.