Remove species from nr

Hi,

I'm using a local installation of blast with the nr database. I'm mostly looking for viral species, but the viral refseq database misses some hits compared to a full nr search, but the nr search takes a long time. I'd like to reduce the time it takes by removing species I don't care about from the database. For example, I'd like to remove all eukaryote DNA from nr. Is this possible? How would I go about doing that?

Thanks!