Developing custom indexing

Hi

I have the following use case:

I currently have a plugin which displays items stored on another webapp which I display in WordPress. I would now like to make these remote items searchable within Solr using your plugin. To do this, I need to retrieve the remote items then hook into your indexer so that I can index the retrieved items in your Solr index.

Is there a way to do this and, if so, are there any API or how-to docs on extending the Solr Search for WordPress indexer?

Any help much appreciated.

Thanks

Hayden