I haven't played with display in div yet, but there are other alternatives to what you are trying to do. I will leave it to you to decide on how elegant that is.
I am assuming you have a relationship of Parent may have one or more Child. (Parent.omChildren)
You could create a peer single Child relationship (Parent.psChild). Peer singles can be displayed as a grid, combo value or form (and others)
You then create a specific form on the Child BO and on the parent have the Parent.psChild display as that form from the Child BO.
Create a specific form for Parent for the creation of Child records using that psChild displayed as form
Then
Create Child with Child.obParent
Parent.psChild=Child
Display the Parent Form with the psChild sub form.
Edit and save with a process after the save to set Parent.psChild =UNDEFINED and display the original Parent form
The psChild attribute would just be for the temporary creation of the child element. It may (you will need to test) automatically create the psChild record for you when you open the Parent form showing psChild form, I can't remember. One caveat is that the subform is not a great solution if you have cascading drop downs there is an unresolved issue where the form refreshes and the initial field is blanked when you select the second drop down and it will not handle multiple nested sub forms ie the form for Child cannot have its own child records displayed as a form.
EDIT - in a multi user environment this will cause contention errors. E.g
User 1 edits parent with child 1, this inserts Child 1 into Parent.psChild
User 2 edits parent with child 2, this inserts Child 2 into Parent.psChild
User 1 saves
User 2 attempts save and gets an error that another user has updated the Parent.