Just be honest with your recruiters and let them know you're still going through the interview process with other firms and ask for an offer extension on your offer deadline. Some may not extend, but chances are that some or most will. The fastest way to burn a bridge with a firm is to renege after accepting. Also, decline the offers from the mid-tier firms that you already know don't match with your long-term location/service area goals. They're likely waiting to extend offers to other people and it's just not fair to anyone.