The least ASB way of making India majority Anglo-Indian is to allow for a three-way partition: one Muslim state, one Hindu, and one Anglo-Indian. Call the Muslim state "Pakistan," the Hindu state "Hindustan" or "Bharat" and call the Anglo-Indian state "India".
Now, where will India be located? Apparently, the British had plans of moving the Anglo-Indians (population in 1947: ~2 million) to the Andaman and Nicobar Islands. I guess that plan did not succeed because I don't think two million people can actually fit in the Andamans without the need for skyscrapers and environmental degradation. Maybe try and increase the Anglo-Indian population by a million or two, forcing the British to carve out a state called India somewhere on the subcontinent.