Cutting the breasts off pigeons involves a certain amount of wastage, as you can never get really tight to the breastbone, and as you say, it can be quite messy.
I prefer to leave the meat on the bone, ending up with just the crown.
All you do is cut the head and wings off close to the body, then peel the skin back from the crop end until the point of the breastbone is revealed.
Press your thumb just under the keel, and literally tear the crown from the carcass.
It sounds really gruesome, but you are left with a neat little package that can be easily frozen, or used straight away.