The simple answer.. you don't.

The advanced answer.. you use the -q and/or -k command line options to include directories in a hierarchy. For example:

• Create a directory called 'usr' in your Sauerbraten directory
• Extract the contents of a package into this 'usr' directory (for this package, you would need to create 'usr/packages/models/monster/ogro' and extract into there)
• Run Sauerbraten with the command line '-qusr', like so: sauerbraten -qusr

If done correctly, Ogros will now look like Spiders.