Take a backup before the race starts, then when you've had enough, suspend the race, then make another backup, then re-load the previous backup, and you're good to play normally. Then, when you want to resume, just re-load the 24h game save.
Now, as cool as this idea sounds, after thinking a little about it, it seems that it could create quite a problem.
1. Save game, pre-race, and back-up to USB drive.
2. Start endurance race on 12/22/2011.
3. Suspend endurance race and back-up new save file.
4. Load previous, pre-race save file.
5. Play GT5 as usual.
6. Reload back-up of suspended endurance race save and it overwrites the latest save data.
Even if you now make a back-up of the current save, there will never be a way to combine the two saves. So, the user will lose anything that he does during the time that he plays the game, even if he backs it up after.
As soon as he reloads the suspended endurance race, the game reverts to the exact point in time that he suspended it. I guess, as long as he doesn't buy a bunch of cars or grind a ton of money or gear or whatever, then it wouldn't matter.
I could definitely see this working if all I was going to do with the game, while the suspended race is backed-up, is play online and didn't really care about the credits and xp earned during those races.
Unless I am misunderstanding, which is highly possible as well.
