You must install the entire calibre package, or none of it. However, one alternative is to use a regular server, with
http://calibre2opds.com to create a plain old html catalog.
Also, be aware that calibre cannot use a library located on a NAS, and will silently fail to update information. Then you will find out, when your books cannot be found, that something must be wrong. Some people have got it working, purely by luck and the phase of the moon, but it's not something you want to rely on. Sync the folders, or at least make sure the calibre computer is the one which own the files.