In your first post you said you were getting the information from logs. This is a great starting point because it means you've got the full User-Agent information right there in front of you. What do you see?
:: counting on fingers ::
200 x 10K = one 2MB file
I am inclined to agree with the rest of wilderness's eloquent assessment.
Logging headers is straightforward in requests for pages, because you can shove the function into your footer code. I use a simple version that was posted here by, I think, incrediBill. I don't know how to do it with non-page requests, but that's not to say it can't be done.
Edit: You could put in a user-agent block on requests for the relevant files. But I think it would be more appropriate to look at the value of the Range header-- this can be done in mod_rewrite, mod_setenvif and possibly other places-- and disallow the file based on header content. As an alternative to outright disallowing, you could redirect requests to a custom page explaining why it won't work.