Took the chance and just put baby with the bigger chicks.. So far, so good- nobody seems to want to bully it and it's making happy chick chatter. I did put the lesser heat lamp at the far end of the brooder because that's where the older ones hang out and it seems to want to hang with them.. They'll just have to be warmer than they'd like for now until this one gets some fat/feathers on it.
Good Luck to the littlest one, and, of course, all of them