Unzipping large ZIP files

I want to unzip an EPUB which contains a lot of big image files.

The EXProc extension step pxp:unzip
<http://exproc.org/proposed/steps/other.html#unzip> seems to require that I
unzip the image files as base64-encoded c:data elements which I then have
to p:store. This loads all the images into memory.

I want to basically unzip all the contents of a ZIP file to a directory
without loading all its contents into memory. Is there a way to do this
that I'm missing or do I have to implement a custom extension step for this?

If unzip gets standardized into XProc 2.0, could a "target" or "output-dir"
option maybe be added that allows unzipping directly to a directory instead
of a c:data element?

Regards
Jostein