How to go from a full pigeon to just the breast
I'd butcher the bird in three portions:


Use the breast as in your recipe.
Remove the legs, set them aside.
Roughly chop up the carcass and make a fonds, then stew/braise the legs from (2.) in it.


If the usual Christmas hustle and bustle doesn't allow a long cooking session now, I'd freeze the carcasses and make the fonds another time, perhaps with a few other delicious scraps. In this case, de-boning the legs (fiddly work, I know) and searing them together with the breasts is an option, or you could decide they are so small that they aren't worth the effort and use with the rest of the carcasses.