They did actually, by putting padding around his waist. Elvis only started gaining weight the last 3 years but only got a lot bigger his last year. If you look at pics of Elvis, his arms and legs are thin and the weight is all gut and water retention. He was very sick at this time as he couldn't expel waste anymore. He needed surgery which he kept putting off and to stop the sleeping pills which he had become dependent on.
This was Elvis with his gf on December 1976 btw: