Easy to do on Arkham Asylum:
1: Start a new game using an
online GFWL profile & after the game autosaves at least once quit to the desktop.
2: Now find the savegame folder & backup the
Save0.sgd savegame file.
3: Now copy the
Save0.sgd savegame file from your old OS install into the new savegame folder & start the game it will find it as long as your using the same GFWL online profile it was created with no need to backup up Xlive folder (although you can do incase other GFWL games need it)!
The gamesave foldername changes with each OS install & gamertag used as long as you copy the contents of it only & use the same GFWL gamertag profile it will work ok.
The whole GFWL ate my gamesaves urban legend was started a few years ago because some players used a pirated version with an offline GFWL profile then found using a legit version with an Online GFWL profile meant the savegame was not transferrerable

as they are 2 different gamertag user accounts