Not all of India, just Northern India, the south is Dravidian mostly. Sorry, I am a nitpicker.
Okay down to business, the Hephthalites don't attack the Gupta Empire (or don't exist) and the Guptas spread through all of India. From there they land themselves in Indonesia on there conquests or trades. Perhaps it becomes a language of aristocrats and important for traders to know if they want to trade. The hardest part is crossing Australia, it was still dominated by aborigines, no economy to help spread it. So unless you want to do a Gupta super-wank I don't see an option. Although perhaps a Gupta-wank followed by a Srivijaya-wank (you just have to make Srivijaya an Indo-European speaking nation and have them colonize Australia).
You still don't have much possibility for the natives though.
EDIT: Also to ward off skepticism before hand, a Gupta-Wank would butterfly the Chola Empire so the Srivijayan Empire would survive long enough to wank.