I think they will tell you to write a letter to the INS Officer. The name of the INS officer is on the upper left of your DOS letter. We did write to the officer, and we used the Fedex to send to the officer directly.
we sent our letter from DOS and the DS1029 with the letter too.(sometimes they probably lose the letter from DOS). We got the receipt 2 weeks later.
You are welcome to contact me for more imformation.
My msn is koconut@163.com.
Good luck with that!
PS: I think without INS receipt you can still apply for your H1B. But it's better to have one.