I have a laptop which needs proprietary drivers (yes, I know). These are known to work on 12.04 but not other versions. I've seen install guides and so on where people say that they could not get 13.10 to work via its installer (and indeed neither could I) but 12.04 did work. Some people have successfully upgraded from 12.04 to 13.10 via the intermediate versions, with a bit of effort.
My problem is that every upgrade guide I have read says "just run upgrade-manager -d". From 12.04 the upgrade-manager only gives me the option to upgrade to 14.04 directly. So, how do I get from where I am to 12.10?