This would get better responses in the Diamond Club forum

some things to consider

a) book one-ways instead of return flight because there are no fuel surcharges ex-Brazil, saving about 200GBP
b) book from a European gateway instead of the UK - save APD.
c) stopover in GRU is most definitely allowed, in both directions if booking one-ways if needed
d) for availability, search continental.com (book reward button) and aeroplan.com (includes Swiss)
e) only call the Indian Call Centre when you have a route planned out ahead of time - or you will be very frustrated
f) your "taxes" will be could be GBP500+ if you fly out of the UK, and book a roundtrip. Most of it is a fuel surcharge.
g) Availability should not be an issue if you are willing to connect in any of: Europe/USA/Canada.