You could try the coffee (or tea) cup method. It has worked for me.
Make a sling to fit across the opening of the cup, with slits cut in it for the chick's legs. I used a wide strip of that stretchy first aid wrap that sticks to itself, and then taped it to the outside of the cup to hold it - but you could use a scrap of fabric and a rubber band just as well. Position it so that the chick will be facing the handle of the cup, and leave a gap at the rear so the chick can poop into the cup.
Put a folded or wadded paper towel in the bottom of the cup so the chick's feet have something to stand on and build strength (and to absorb poop).
Put the chick into the sling, and hold it there while you apply another WIDE strip of the first aid wrap across its back, attach it to the cup, and make it snug so the chick can't wiggle out. You could use any other material I suppose, but I like the sticky wrap because it holds the chick better and doesn't harm the down. (Next time I have to do it, I'll cut a hole for the chick's head, too, to help hold it in place.)
Make a tiny feed cup and water cup using soda bottle lids or what-have-you. I used some old plastic measuring spoons with the handles cut off. Tape those together (duct tape is great), and then tape them to the handle of the cup so they're within the chick's reach. Fill with food and water.
Place the cup into the brooder or incubator - depending on what kind of heat source you have, you might have to improvise. I used a heat lamp, so it was easy to set the cup at about the same position as all the other chicks were hanging out; not under the lamp, but not in the cold either. Whatever zone the other chicks are relaxing, is the same place you want to put the chick and cup. I had to place the cup and chick inside a bigger container so that the other chicks wouldn't mess with him, but they could still hear each other. And then watch closely so he doesn't get overheated or cold.
The chick will struggle to get out, kicking and stretching his legs. GOOD. He's getting physical therapy. YOU can also provide physical therapy by holding the chick over a non-slick surface, legs between your fingers, and make him use his legs in the correct position to build strength. 15-20 minutes per session, several times a day.
I hope this helps.
(Disclaimer: I've never successfully done the PT myself, but have read this is how it's done. I also have only tried to rehabilitate ONE chick using the cup method, and it was successful.)