This has been discussed here numerous times. A few days ago, someone posted about travelling to India on Indian PP and then trying to book an appointment in India for its cancellation. You may want to search the forum to see if they have provided an update.Isn't it true you can use your Indian passport for upto 3 months since becoming a foreign citizen?
"A grace period of three months is allowed from the date of acquisition of foreign citizenship, for the purpose of travel on an Indian Passport. Therefore, no penalty will be leviable for travel on an Indian passport within three months of acquisition of a foreign passport. "
Knowing Indian babudom, I'd hate to try out a grace period option which no one really knows much about.