I've found that putting them in the fridge JUST before they're ripe and pulling them out a few hours before you need them is the best way to go. That, or mashi

I've found that putting them in the fridge JUST before they're ripe and pulling them out a few hours before you need them is the best way to go. That, or mashing them up ahead of time and freezing. Avocados freeze very well due to their specific make up.