He'd have to do something pretty bloody spectacular to get a constitutional amendment passed just for him. Like end the Korean War before it starts by flying over there and defeating Kim Il-Sung in a no-holds-barred wrestling match on the top of an airship flying over Moscow. His impressive finishing backbreaker scares Stalin, Ho Chi Minh, and Mao into becoming capitalists.
Seriously, though, he'd have to do something to become so wildly popular that the public demands his return. I'm hesitant to suggest ending the just-started Korean War with nukes and making some kind of impressive speech showing everyone the US is tops, but it's all I can think of for July 1, 1950.