Just offer Proxy server access as an alternative for file downloads. Then it only downloads once per community. SQUID is well known, and FREE. This technology was used for years before the advent of high speed everywhere; but it is still valid where necessary. Once configured, just forget it.
http://www.david-guerrero.com/papers/squid/squid.htm
For extremely large files, a separate WEB server or FTP server with a fixed IP might do the trick. Just place the files by DVD on the server, and download them over the local WAN. Cool. Can be implemented with a simple Windows Professional Version PC.
http://www.labnol.org/software/browse-websites-faster-on-slow-internet-connections/8059/
Community Caching
http://httpd.apache.org/docs/1.3/mod/mod_proxy.html
