It can be done, but any methods to do so are likely to be ad-hoc, involving both surface treatment and/or anodizing process optimization. Cast Al alloys are designed for fluidity and ease of casting, and not primarily for surface properties. Melt-fluidity is achieved through alloying additions (mostly Si). Upon solidification this Si does not anodize. This is a part of a larger category of problems: the surface of the cast is not uniform/predictable enough to anodize in a well-behaved manner.

There seems to be no universal prescriptive strategy for anodizing die-cast Al products. There are two major obstacles: (a) the complicated chemistry and topography of the cast surface, and (b) optimizing a non-standard anodizing bath, which potentially involves trial-and-error. Getting around these problems will incur additional capital costs, so the economy of die-casting can be easily offset.  

As a default stance, one should remain critical of claims regarding 'easy' methods of anodizing die-cast Al surfaces. These claims of success may have traded surface-appearance for reliability, or may have extensively tweaked the post-casting surface treatment and process parameters for a specific alloy. 

Overall, innovative methods of anodizing die-cast Al alloys aren't impossible, but are difficult to optimize for properties (corrosion-resistance+aesthetics+surface integrity).  

More detail information: http://..........com/contentimages/features/Compcote_AIT.pdf

Corrosion protection for die-cast Al: Pioneer Metal Finishing - Die Cast Finishes