Comment 1 for bug 286312

Have you tried adding it as a regexp in /etc/apt-cacher/apt-cacher.conf there is a section (repated below) that should make it trivial.

# Permitted package files - this is a perl regular expression which matches all
# package-type files (files that are uniquely identified by their filename).
# The default is:
#package_files_regexp = (?:\.deb|\.rpm|\.dsc|\.tar\.gz|\.diff\.gz|\.udeb|index\.db-.+\.gz|\.jigdo|\.template)$