Have him nominated in 1932 instead, although the race will be far closer, I think Smith would be able to limp across the finish line.
I agree that Smith would win in 1932. The problem is that it is precisely in a year like 1932, with victory in sight, that the Democrats would be unlikely to nominate as risky a candidate as Smith. In 1928, one reason he won the nomination so easily was that Hoover was heavily favored anyway, so the Democrats figured that they might as well take a chance on Smith.
The nomination of Smith was particularly unlikely in 1932 in OTL of course because of the memories of how badly he had done in 1928. If Smith had passed on the presidential race in 1928 and remained governor of New York, he would have two advantages for 1932: First, of course, he would not have the landslide loss of 1928 to live down; and second, Franklin D. Roosevelt, not having been elected governor of New York, would not be a plausible candidate, even if he broke with Smith. I doubt that the Democrats would nominate Smith in 1932 even under these circumstances, but his chances would be better than in OTL.