I got lucky this week. A couple of months ago, just as rumours of Avios were surfacing, I booked LHR-GIG/GRU-LHR in CW for April as I wasn't seeing anything for EZE. We're planning to go from Rio to Iguassu to Buenos Airies and then we would have had to back track to Sao Paolo and given that we wanted as stress free holiday as possible, we would have gone the day before to GRU to ensure no missed connections.
After daily checking of the EZE-LHR in April I checked LHR-EZE in May. There was a friendly date GIG-LHR available also so I called on Monday morning and swapped the bookings over. By shifting it 3 weeks and "reversing" the trip I'm saving £££ in additional airfares and hotel costs, plus saving time by not going to GRU. There was still availibilty later in May when I looked yesterday.
As they always say on here, get as near as close to your ideal trip dates if they become available and then keep checking! Even though I could have saved 10,000 miles when the GIG redemption level reduces post Avios, I'd rather know I have the trip booked and secured. Good luck with your hunt for tickets!