Found the little ratapignata! This is indeed a great little spot for a bat, although she does seem to be roosting elsewhere now that she's okay. I've named her Ella, which is a Nissart name. She's too cute not to be named, just look at those adorable ears. I've contacted the local office of the environment here to ask if they have bat houses, since I remember them distributing some last year. In the meantime, the kitties stay inside while Ella sleeps!
Update here: perso.fraise.net/permalink/2012/07/1499/