Opening a follow up form at the end of registration or opening a form with android callout

Dear

I have a use case where I want to have 1 registration and 2 followup (1 and 2)

in most of the case the registration should directly be followed by followup 2
but in the other cases, the user should wait and come back later to this case; then he will open followup 1 directly followed by followup2.

I want to have this behavior because follow up 2 is complex and I don’t want to duplicate it in registration and followup 1; it will ease also data reporting.

Is it possible to start a follow up form from for a given case directly at the end of the registration ?

If this is not possible within commcare, do you think it will be possible trick the system by calling commcare with an android callout where the form and caseid could be passed as callout param ?

Best regards