Most Helpful Girl
Try putting it out there that you are seeing someone from a different school. Don't be specific, just bring up in conversation that your "girl" and you did XYZ. You only need to tell one, the rest will hear. Yeah, lying sucks but if there is more than one girl interested it is a blanket fix for all of them. Best way to not hurt anyone.
Most Helpful Guy
Buy some of those custard pies and just throw em at their faces.