I have never tried this, but my Update Manager's Software Sources has a line (not checked on my system) "file:///usr/share/local-repository" in the Other Software tab. I assume that you could download the files manually, place them into that directory, and enable that directory as a repository.
Hmm. Not sure how you would get your computer to realize that there is an "upgrade," though. Maybe do it through Synaptic (or a terminal) once you have grabbed the files and enabled your local repo?
Mint 17.1 Xfce 4.12.
If guns kill people, then pencils misspell words, cars make people drive drunk, and spoons made Rosie O'Donnell fat.