Well if you want Spain to not be at war when the Philippines has their uprising, I don't think any country will want to get involved and needlessly provoke a declaration of war or something from Spain.
One way of making intervention 'justified' could be to have the Spanish commit a lot more atrocities in the Philippines and, perhaps more importantly, for the world press to give a damn about it (maybe the hostility between Spain and the USA can play a role here).
Philippine revolutionaries then seize Palawan, but their strength is dwarfed by Spanish forces. So with nowhere else to go, they offer to cede themselves to the Brookes or something. In that case, maybe the sheer revulsion against Spain for their massacres comes into play, and the British 'broker' a deal in which Palawan goes to Sarawak and, in the course of time, to the UK.