Well, there's always making the Partido Nacionalista de Puerto Rico, with or without Pedro Albizú Campos (or something like the Party), become to the island what the Indian Nationalist Congress was for the Raj. If you bring the Nationalists into political power early enough - combined with nonviolent civil resistance similar to Gandhi's satyagraha (leading to reactions on the Mainland similar to what happened when the US tried to crack down on the insurgency in the Philippines, which was basically total outrage) - that would make the difference. It would basically be the end of the Raj on speed, combined with the wider Latin American historical context due to dissatisfaction with Cometan positivism (which, although Washington did not realize it, was basically what their colonial rule was) leading people in the region to seek alternatives, and with Puerto Rico in particular feeding on dissatisfaction with being granted American citizenship since it was seen as feeding the conscription pool for the US Armed Forces for WW1. In such a context, the Nationalists could feed on the anti-conscription feeling on the Island and use it for trying to achieve independence by peaceful means. Then, once our FDR equivalent comes on the stage, seeing as the 1930s was when the US pulled back from occupying various Latin American countries, at some point Puerto Rico too would be swept up in this wave - even if it means something similar to what would soon exist for the Philippines (which was basically the Commonwealth model as originally intended, as a transitional stage to independence), at first.