BUILD and how to create a subclass object when creating a parent

Hi,

I tried to use the BUILD method to create an instance of a subclass on 
creating an instance of the parent. This does not work and the 
documentation clearly explains why:

http://search.cpan.org/dist/Moose/lib/Moose/Manual/Construction.pod#BUILD_and_parent_classes

BUILD methods are called from parent to child and hence this triggers a 
loop.

I am able to do this with the around method modifier, however I need to 
override the behaviour in the subclass. This is also seems error prone 
and bad practice.

But if this cannot be done this way, how should it be done? How can I 
always create a subclass instance on creation of it's superclass?

Kind regards,

Arjan