It doesn't matter if the files are local or remote, ngx_pagespeed can fetch from both. Some docs on related functionality: https://developers.google.com/speed/docs/mod_pagespeed/domai...
Edit: Looking over your build files. I think I'm going to go ahead and create (or modify existing) spec files and throw together a github for an nginx RH tree. If anyone is interested in it when done, shoot me an e-mail through profile.
https://github.com/justicel/nginx-pagespeed
Pretty sure github is going to yell at me about the binary files :P
I tried the scripts verbatim on a fresh Ubuntu 13.04 VM (64bit).
edit: Your deb link at the end of the readme is broken as well.