Having not done this myself, I’d think you could use your last 10.7.x back up to restore after a clean 10.7 install + update.
Obviously this could be problematic if you don’t have a copy of the Lion installer handy as, to my knowledge, it’s no longer available from Apple.
Definitely google downgrade or roll back to lion (or something to that effect) first to see if others who actually have tried it have had success and what the issues are. You don’t want to get caught missing something mid way through.
Apple’s discussions/support threads and macrumors forums are probably decent places to start for more in-depth info. With a quick check I’m pretty sure I also saw a link to a youtube video about downgrading from 10.8 to 10.7.