I had my OPT Expedited in December 08. Believe it or not, it was approved in 2 weeks.
basically all u need to do is explain how losing this job will be a setback for you, not just financially but to your career as well.
I had following docs. with me when I sent my OPT Expedite request:
1. All necessary documents ( typical for a regular OPT application)
2. Offer Letter stating clearly that they need u by certain date for reasons like they have shortage of employees, a major project coming up or anything that u think is suitable
3. A letter by the DSO recommending Expedite
4. A letter by you ( the student) explaining how this job is so important for your career and if u dont get OPT by some date you might lose your job for which u worked so hard and the loss will not be mere financial.
Any questions shoot me e-mail Prabhatkarna@yahoo.com. I will be happy to help.
Best of luck and God bless.