Editing subform within a subform

Editing subform within a subform

Hi,
I've got three forms:
- Parent registration form
- Child registration form (subform within parent registration form)
- and Program registration form (subform within child registration form)

I've shown it pictorially below:

I'm wondering whether I can get the child registration form to open as a popup dialog so that I can allow users to add program registration data to the child registration subform.

Has anyone faced this issue before? Any ideas?