From the Kay Erdwinn’s Post Teaching Yoga for Round Bodies
This is another asana that my neck protests, so I myself don’t practice it. The main problem(s) for the fat person would probably be once again getting the elbows in enough to provide the necessary leverage, plus the sheer amount of weight that must be supported by the arms/wrists, which is a difficulty even for many thinner students.
When I was first learning this asana, I would lift my torso, then blithely sway, putting weight on first one shoulder, then another, in order to move the elbows in. It made the asana possible for me, but I was doing heinous things to my neck in the process. I have seen other strong fat people attempt the same maneuver, and I’ve had to rush to stop them. It’s frustrating for the fat student who is otherwise ready to try the asana.
A way around the difficulty is to practice against the wall or with a chair. With the buttocks and feet resting against the wall, legs bent, it is possible to support some of the weight via the legs instead of the hands, just enough to shift the elbows in without torquing the neck. However, it could place a little extra flexion strain on the neck, so one must use caution.
The notes about blankets mentioned for Halasana also apply here.