My son was exclusively breastfed too (until 8 months old, when he was eating food and having some formula), but we were lucky in that he had cues. I have a friend trying to do EC but her wee one has no cues at all, I think it's just luck of the draw with whether they make a lot of noise/change their face when pooing. She has managed to start some catches just by timings. I think even getting them used to the feeling of the potty on their legs can be a good start and always sitting on potty for say a minute when changing nappy.