Include a custom processing step between asciidoctor and the backend?

Hi there,
we are trying to use asciidoctor for generating deck.js slides from our graphgists, see gist.neo4j.org for the default client-side rendering with Opal.js.

Now, we are preprocessing the asciidoc and inserting pass-through blocks for som of the comments we have added in order to find them in a post-processing step and insert custom HTML functionality.

Running now server-side, we would like to do the same thing. Is there any way to insert a custom processing step between the generation of asciidoc (e.g. pulling in the includes) and handing it off to the backend (deckjs in our case)?

Right now we are running

asciidoctor -T ./asciidoctor-backends/haml/deckjs -a allow-uri-read -a presenter="Your Name"  index.adoc

but when we get to deck.js templates, the comments are gone already ...

Thanks for any hints!

/peter