Network, network, network. No matter how high your GMAT, there will be plenty of other candidates who have equally impressive scores so there's no way to stand out purely because of your score. Use any connections you have with people at the firms - friends, friends of coworkers, alumni of your school, firm employees recruiting at your school, etc. - to talkto as many people at the firm as possible. More than anything else, you need to recruit people inside the firm to bang the table for you that you deserve to work there, especially coming from a non-target school.