8老师,皮老师: 485 RFE 中permanent position, 如何回复

8老师,皮老师,终于看到485RFE mail. It is basically asking to prove the portablity based on AC21. Other than demonstrating that I am working at similar field, I have to show that this position is permanent. However, I know my employer will definately not put down this statement. What I was recommended to put down is the at-will postion with indefinite duration. Do you see any problem? Anyone has similar experience? Thank you so much!!