Agustin,
I have had success using a 'regular' subform as the Overflow Leader.
In the initialize event, I set the subform as hidden.
This subform is defined at the same level in the hierarchy as the flowing main subform.
In the Layout:Ready event, I test the xfa.layout.page(this) property, and if > 1 - set presence as visible.
Reference the subform as the Overflow Leader in the Pagination Properties of your flowing subform.
I use global bindings on the fields within the overflow leader so that the data is in sync with the XML payload being merged with the template.
Initialize:
this.presence = "hidden";
Layout:Ready:
if ( xfa.layout.page(this) > 1 )
this.presence = "visible";
else
this.presence = "hidden";
Hope this helps
Mark