I did it in 2005 – my first ever sportif! Trained hard from January, solo hilly 100 milers most Saturday mornings and got my weight down to 10 stone (at 5’11” I didn’t look great that light, my wife hated it).
Went with the aim of getting a Gold finish, and managed it by 7 minutes. One thing that helped me was I’d practised dressing and undressing (wind top, arm warmers etc) whilst riding – as I needed to do this at the top of every descent and bottom of every climb this saved me a fair bit of time. Ate and drank on the go to, I only stopped to piss (once on the whole ride- hmm perhaps I wasn’t drinking enough).
The final climb of Alpe D’Huez was the most miserable experience ever on a bike, I was close to tears most of the way up I was so mentally and physically exhausted. That said, it was an amazing experience, overall I loved it, and I’d do it again if I could be arsed to get fit enough.