You can EASILY loose 5 pounds of water via the sauna before your weigh in. I have done this with clients many times when they need to make a bodybuilding class.
The day of the weigh in, don't eat or drink anything. Sit in the sauna until you meet your weight requirement. After the weigh in, focus on rehydrating and eating to fuel yourself for the fight.
If you only have a week, that's going to be your best bet.