The key point here is India. India, India, India. It was the largest, most populous, and richest of the non-Dominion Empire states. If you keep India in somehow, you keep the Empire (which, after all, was there to support India). If you don't, it's all going away sooner-or-later, at least anything but remnants.
The best way to do this, IMHO, is for the Brits to not be quite such bastards early on, and more-or-less rapidly move towards a Dominion India post-WWI. Of course, there would need to be cooperation amongst the Dominions ITTL, at least much more than there was OTL, but that can probably be arranged. Plus, as that involves ministerial etc. meetings rather than a Parliament, the delicate question of Indian dominance can be deferred some time.
The best way to do this, IMHO, is for the Brits to not be quite such bastards early on, and more-or-less rapidly move towards a Dominion India post-WWI. Of course, there would need to be cooperation amongst the Dominions ITTL, at least much more than there was OTL, but that can probably be arranged. Plus, as that involves ministerial etc. meetings rather than a Parliament, the delicate question of Indian dominance can be deferred some time.