Apart from killing the guy somehow, somewhen, somewhere - the best and IMHO rather automatic possibility is another death. It is not so implausible that the rather aged Hindenburg dies a few years earlier. If there are presidential elections to be held between 1928 and early 1931, there would probably a new Reichspräsident either belonging to the democratic parties (Marx again?) or someone moderately right-wing (Lettow-Vorbeck e.g.).
Having the 7-year-tenure in mind, such a president could ride out the Great Depression, not having to fear elections until 1935/38.