Not really i think. The model is the only place that setting can be changed - and it would affect all docs of say type "cm:content" - which most would derive from.
It is possible you could configure in a content transformer class that purposely returning nothing for specific mimetypes i.e. if the documents you don't want indexed are all of a specific mimetype that it could probably be done, but it would require a custom java class configured in.
Thanks,
Kevin