How Do Erg langs handle causative? Was: Re: Active

> One reason for me to have little sympathy with stadialists is how they
> treat obvious examples of the opposite direction of development. For
> instance, they insist that modern Indo-Aryan languages (mostly ergative,
> but descending from the nominative Sanskrit) are only 'formally', but not
> 'truly' ergative. One of the favorite stadialist arguments is that
> most Indo-Aryan langs have causative, which (in their opinion) a 'truly
> ergative' language should not have.
This got me interested. How does a 'truly ergative' lang handle causative
transitive constructions of the kind "I made him buy it" according to them?
(For surely, they must be able to handle them in some way).