Look, if someone gets that fat, simply don’t feed them.
Since they can’t move, provide them with WATER ONLY. They WILL lose enough blubber to allow them to walk again long before they starve.
No, they will die.
And they won’t have any muscle left to walk before they die.
They won’t loose much fat at all.
The only way to loose fat is to turn it into muscle and/or feed muscle. Exercise. Every bit counts.