Idoc Extension Question

Hi Guys

i am trying to extend standard Idoc DELVRY03 to add a z segment to it.i want it to be a child segment of E1EDL20 but i want it to be right at the bottom after E1EDL54.can this be done?i tried adding it to E1EDL20 and it stays right at the top of it i want it at the bottom i can have it as a child to E1EDL54.but as i said i want it to be a child of E1EDL20 and be the last segment.Please if someone can suggest something it would be great.

Thanks a lot in Advance