ncprasad, I faced the same problem with my company, 6+ years in one company only.
For Stanford I filled out one employer, and used the 350 CHARACTERS (yes, characters, NOT words) to describe my responsibilities, challenges and accomplishments (350 characters each). It was tough, but when I did it, I realized any more words is just extraneous.
For Haas, I'm filling it out as one... I forgot what the format is, but I think I got enough in there to show progression... it was a bit tricky. I hope my resume will show them progression better than the work history input. They can't expect people to show all progression in the tiny space they give!
The question I have for Haas is how DETAILED of a part-time work experience from college do they want?