Short answer: no.
Longer answer, if they are disabled and fat, go ahead. But I'm afraid that may be the exception, not the rule. I'd be interested to see some investigative reporting done, focus being doctors that give out handicapped stickers for the sole reason of obesity.
I've known quite a few fat people in my life, and most of them don't have much trouble getting around, so I have rather limited sympathy for "obesity" as some kind of disability. In fact, if you are in your 20s or 30s, I file that more under "personal choice" than "disability". Not trying to be judgmental, but I've seen people in their 60s lose a ton just by cutting their flour and sugar intake.